split formatted I/O header, unify undefined behavior reporting with UNDEFINED_FMT() macro

67 files changed, 184 insertions, 136 deletions

diff --git a/mk/__conv.d b/mk/__conv.d
index 3512ad7f..93c8552d 100644
--- a/mk/__conv.d
+++ b/mk/__conv.d
@@ -3,7 +3,7 @@ libc.a(__conv.o): $(OBJDIR)/__conv.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/__conv.o: src/stdio/__conv.c
-$(OBJDIR)/__conv.o: src/stdio/_stdio.h
+$(OBJDIR)/__conv.o: src/stdio/_format.h
 $(OBJDIR)/__conv.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/__conv.c
diff --git a/mk/__printf.d b/mk/__printf.d
index 472b91b5..f6e20da6 100644
--- a/mk/__printf.d
+++ b/mk/__printf.d
@@ -4,7 +4,7 @@ libc.a(__printf.o): $(OBJDIR)/__printf.o
 
 $(OBJDIR)/__printf.o: src/stdio/__printf.c
 $(OBJDIR)/__printf.o: src/_forced/strdup.h
-$(OBJDIR)/__printf.o: src/stdio/_stdio.h
+$(OBJDIR)/__printf.o: src/stdio/_format.h
 $(OBJDIR)/__printf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/__printf.c
diff --git a/mk/__scanf.d b/mk/__scanf.d
index 930313ea..fe2530d2 100644
--- a/mk/__scanf.d
+++ b/mk/__scanf.d
@@ -3,7 +3,7 @@ libc.a(__scanf.o): $(OBJDIR)/__scanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/__scanf.o: src/stdio/__scanf.c
-$(OBJDIR)/__scanf.o: src/stdio/_stdio.h
+$(OBJDIR)/__scanf.o: src/stdio/_format.h
 $(OBJDIR)/__scanf.o: src/_safety.h
 $(OBJDIR)/__scanf.o:
 	@mkdir -p $(@D)
diff --git a/mk/fprintf.d b/mk/fprintf.d
index 59961d11..c9eadc6d 100644
--- a/mk/fprintf.d
+++ b/mk/fprintf.d
@@ -3,7 +3,7 @@ libc.a(fprintf.o): $(OBJDIR)/fprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/fprintf.o: src/stdio/fprintf.c
-$(OBJDIR)/fprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/fprintf.o: src/stdio/_format.h
 $(OBJDIR)/fprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/fprintf.c
diff --git a/mk/fprintf_s.d b/mk/fprintf_s.d
index 933cff73..b54a5f65 100644
--- a/mk/fprintf_s.d
+++ b/mk/fprintf_s.d
@@ -3,7 +3,7 @@ libc.a(fprintf_s.o): $(OBJDIR)/fprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/fprintf_s.o: src/stdio/fprintf_s.c
-$(OBJDIR)/fprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/fprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/fprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/fprintf_s.c
diff --git a/mk/fscanf.d b/mk/fscanf.d
index c99d121b..e2feb8a6 100644
--- a/mk/fscanf.d
+++ b/mk/fscanf.d
@@ -3,7 +3,7 @@ libc.a(fscanf.o): $(OBJDIR)/fscanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/fscanf.o: src/stdio/fscanf.c
-$(OBJDIR)/fscanf.o: src/stdio/_stdio.h
+$(OBJDIR)/fscanf.o: src/stdio/_format.h
 $(OBJDIR)/fscanf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/fscanf.c
diff --git a/mk/fscanf_s.d b/mk/fscanf_s.d
index cfef8588..2961461b 100644
--- a/mk/fscanf_s.d
+++ b/mk/fscanf_s.d
@@ -3,7 +3,7 @@ libc.a(fscanf_s.o): $(OBJDIR)/fscanf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/fscanf_s.o: src/stdio/fscanf_s.c
-$(OBJDIR)/fscanf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/fscanf_s.o: src/stdio/_format.h
 $(OBJDIR)/fscanf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/fscanf_s.c
diff --git a/mk/printf.d b/mk/printf.d
index f6268e62..a8cac79b 100644
--- a/mk/printf.d
+++ b/mk/printf.d
@@ -3,7 +3,7 @@ libc.a(printf.o): $(OBJDIR)/printf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/printf.o: src/stdio/printf.c
-$(OBJDIR)/printf.o: src/stdio/_stdio.h
+$(OBJDIR)/printf.o: src/stdio/_format.h
 $(OBJDIR)/printf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/printf.c
diff --git a/mk/printf_s.d b/mk/printf_s.d
index a81dfe49..514a7322 100644
--- a/mk/printf_s.d
+++ b/mk/printf_s.d
@@ -3,7 +3,7 @@ libc.a(printf_s.o): $(OBJDIR)/printf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/printf_s.o: src/stdio/printf_s.c
-$(OBJDIR)/printf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/printf_s.o: src/stdio/_format.h
 $(OBJDIR)/printf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/printf_s.c
diff --git a/mk/scanf.d b/mk/scanf.d
index 57ee458d..25409a70 100644
--- a/mk/scanf.d
+++ b/mk/scanf.d
@@ -3,7 +3,7 @@ libc.a(scanf.o): $(OBJDIR)/scanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/scanf.o: src/stdio/scanf.c
-$(OBJDIR)/scanf.o: src/stdio/_stdio.h
+$(OBJDIR)/scanf.o: src/stdio/_format.h
 $(OBJDIR)/scanf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/scanf.c
diff --git a/mk/scanf_s.d b/mk/scanf_s.d
index 1a65a5a2..c4fe17e2 100644
--- a/mk/scanf_s.d
+++ b/mk/scanf_s.d
@@ -3,7 +3,7 @@ libc.a(scanf_s.o): $(OBJDIR)/scanf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/scanf_s.o: src/stdio/scanf_s.c
-$(OBJDIR)/scanf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/scanf_s.o: src/stdio/_format.h
 $(OBJDIR)/scanf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/scanf_s.c
diff --git a/mk/snprintf.d b/mk/snprintf.d
index 1ed073a2..79a1d4a4 100644
--- a/mk/snprintf.d
+++ b/mk/snprintf.d
@@ -3,7 +3,7 @@ libc.a(snprintf.o): $(OBJDIR)/snprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/snprintf.o: src/stdio/snprintf.c
-$(OBJDIR)/snprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/snprintf.o: src/stdio/_format.h
 $(OBJDIR)/snprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/snprintf.c
diff --git a/mk/snprintf_s.d b/mk/snprintf_s.d
index b2c1fdbd..805a2d90 100644
--- a/mk/snprintf_s.d
+++ b/mk/snprintf_s.d
@@ -3,7 +3,7 @@ libc.a(snprintf_s.o): $(OBJDIR)/snprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/snprintf_s.o: src/stdio/snprintf_s.c
-$(OBJDIR)/snprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/snprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/snprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/snprintf_s.c
diff --git a/mk/sprintf.d b/mk/sprintf.d
index 384da76c..f42eade9 100644
--- a/mk/sprintf.d
+++ b/mk/sprintf.d
@@ -3,7 +3,7 @@ libc.a(sprintf.o): $(OBJDIR)/sprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/sprintf.o: src/stdio/sprintf.c
-$(OBJDIR)/sprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/sprintf.o: src/stdio/_format.h
 $(OBJDIR)/sprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/sprintf.c
diff --git a/mk/sprintf_s.d b/mk/sprintf_s.d
index 65c99698..dd99120d 100644
--- a/mk/sprintf_s.d
+++ b/mk/sprintf_s.d
@@ -3,7 +3,7 @@ libc.a(sprintf_s.o): $(OBJDIR)/sprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/sprintf_s.o: src/stdio/sprintf_s.c
-$(OBJDIR)/sprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/sprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/sprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/sprintf_s.c
diff --git a/mk/sscanf.d b/mk/sscanf.d
index 3c6aac2c..18723f33 100644
--- a/mk/sscanf.d
+++ b/mk/sscanf.d
@@ -3,7 +3,7 @@ libc.a(sscanf.o): $(OBJDIR)/sscanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/sscanf.o: src/stdio/sscanf.c
-$(OBJDIR)/sscanf.o: src/stdio/_stdio.h
+$(OBJDIR)/sscanf.o: src/stdio/_format.h
 $(OBJDIR)/sscanf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/sscanf.c
diff --git a/mk/sscanf_s.d b/mk/sscanf_s.d
index ec0e0749..490c0a46 100644
--- a/mk/sscanf_s.d
+++ b/mk/sscanf_s.d
@@ -3,7 +3,7 @@ libc.a(sscanf_s.o): $(OBJDIR)/sscanf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/sscanf_s.o: src/stdio/sscanf_s.c
-$(OBJDIR)/sscanf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/sscanf_s.o: src/stdio/_format.h
 $(OBJDIR)/sscanf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/sscanf_s.c
diff --git a/mk/vfprintf.d b/mk/vfprintf.d
index 9aff877d..9f680028 100644
--- a/mk/vfprintf.d
+++ b/mk/vfprintf.d
@@ -3,7 +3,7 @@ libc.a(vfprintf.o): $(OBJDIR)/vfprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vfprintf.o: src/stdio/vfprintf.c
-$(OBJDIR)/vfprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/vfprintf.o: src/stdio/_format.h
 $(OBJDIR)/vfprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vfprintf.c
diff --git a/mk/vfprintf_s.d b/mk/vfprintf_s.d
index 6e63c760..30bbed60 100644
--- a/mk/vfprintf_s.d
+++ b/mk/vfprintf_s.d
@@ -3,7 +3,7 @@ libc.a(vfprintf_s.o): $(OBJDIR)/vfprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vfprintf_s.o: src/stdio/vfprintf_s.c
-$(OBJDIR)/vfprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vfprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/vfprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vfprintf_s.c
diff --git a/mk/vfscanf.d b/mk/vfscanf.d
index caf1f99b..eb9df79c 100644
--- a/mk/vfscanf.d
+++ b/mk/vfscanf.d
@@ -3,7 +3,7 @@ libc.a(vfscanf.o): $(OBJDIR)/vfscanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vfscanf.o: src/stdio/vfscanf.c
-$(OBJDIR)/vfscanf.o: src/stdio/_stdio.h
+$(OBJDIR)/vfscanf.o: src/stdio/_format.h
 $(OBJDIR)/vfscanf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vfscanf.c
diff --git a/mk/vfscanf_s.d b/mk/vfscanf_s.d
index 30c708c6..d9520908 100644
--- a/mk/vfscanf_s.d
+++ b/mk/vfscanf_s.d
@@ -3,7 +3,7 @@ libc.a(vfscanf_s.o): $(OBJDIR)/vfscanf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vfscanf_s.o: src/stdio/vfscanf_s.c
-$(OBJDIR)/vfscanf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vfscanf_s.o: src/stdio/_format.h
 $(OBJDIR)/vfscanf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vfscanf_s.c
diff --git a/mk/vprintf.d b/mk/vprintf.d
index 66825ea0..88d686a8 100644
--- a/mk/vprintf.d
+++ b/mk/vprintf.d
@@ -3,7 +3,7 @@ libc.a(vprintf.o): $(OBJDIR)/vprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vprintf.o: src/stdio/vprintf.c
-$(OBJDIR)/vprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/vprintf.o: src/stdio/_format.h
 $(OBJDIR)/vprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vprintf.c
diff --git a/mk/vprintf_s.d b/mk/vprintf_s.d
index ee2d1d17..fac05326 100644
--- a/mk/vprintf_s.d
+++ b/mk/vprintf_s.d
@@ -3,7 +3,7 @@ libc.a(vprintf_s.o): $(OBJDIR)/vprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vprintf_s.o: src/stdio/vprintf_s.c
-$(OBJDIR)/vprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/vprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vprintf_s.c
diff --git a/mk/vscanf.d b/mk/vscanf.d
index dee498c8..9e10c118 100644
--- a/mk/vscanf.d
+++ b/mk/vscanf.d
@@ -3,7 +3,7 @@ libc.a(vscanf.o): $(OBJDIR)/vscanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vscanf.o: src/stdio/vscanf.c
-$(OBJDIR)/vscanf.o: src/stdio/_stdio.h
+$(OBJDIR)/vscanf.o: src/stdio/_format.h
 $(OBJDIR)/vscanf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vscanf.c
diff --git a/mk/vscanf_s.d b/mk/vscanf_s.d
index 0078e109..37a03f7b 100644
--- a/mk/vscanf_s.d
+++ b/mk/vscanf_s.d
@@ -3,7 +3,7 @@ libc.a(vscanf_s.o): $(OBJDIR)/vscanf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vscanf_s.o: src/stdio/vscanf_s.c
-$(OBJDIR)/vscanf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vscanf_s.o: src/stdio/_format.h
 $(OBJDIR)/vscanf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vscanf_s.c
diff --git a/mk/vsnprintf.d b/mk/vsnprintf.d
index 19fa6b69..6f482567 100644
--- a/mk/vsnprintf.d
+++ b/mk/vsnprintf.d
@@ -3,7 +3,7 @@ libc.a(vsnprintf.o): $(OBJDIR)/vsnprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vsnprintf.o: src/stdio/vsnprintf.c
-$(OBJDIR)/vsnprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/vsnprintf.o: src/stdio/_format.h
 $(OBJDIR)/vsnprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vsnprintf.c
diff --git a/mk/vsnprintf_s.d b/mk/vsnprintf_s.d
index 72f8afbf..92d6bc51 100644
--- a/mk/vsnprintf_s.d
+++ b/mk/vsnprintf_s.d
@@ -3,7 +3,7 @@ libc.a(vsnprintf_s.o): $(OBJDIR)/vsnprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vsnprintf_s.o: src/stdio/vsnprintf_s.c
-$(OBJDIR)/vsnprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vsnprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/vsnprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vsnprintf_s.c
diff --git a/mk/vsprintf.d b/mk/vsprintf.d
index e449cd0f..b4af0dec 100644
--- a/mk/vsprintf.d
+++ b/mk/vsprintf.d
@@ -3,7 +3,7 @@ libc.a(vsprintf.o): $(OBJDIR)/vsprintf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vsprintf.o: src/stdio/vsprintf.c
-$(OBJDIR)/vsprintf.o: src/stdio/_stdio.h
+$(OBJDIR)/vsprintf.o: src/stdio/_format.h
 $(OBJDIR)/vsprintf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vsprintf.c
diff --git a/mk/vsprintf_s.d b/mk/vsprintf_s.d
index 806a6e70..3add5ac1 100644
--- a/mk/vsprintf_s.d
+++ b/mk/vsprintf_s.d
@@ -3,7 +3,7 @@ libc.a(vsprintf_s.o): $(OBJDIR)/vsprintf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vsprintf_s.o: src/stdio/vsprintf_s.c
-$(OBJDIR)/vsprintf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vsprintf_s.o: src/stdio/_format.h
 $(OBJDIR)/vsprintf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vsprintf_s.c
diff --git a/mk/vsscanf.d b/mk/vsscanf.d
index b6ebc798..a0d6af5a 100644
--- a/mk/vsscanf.d
+++ b/mk/vsscanf.d
@@ -3,7 +3,7 @@ libc.a(vsscanf.o): $(OBJDIR)/vsscanf.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vsscanf.o: src/stdio/vsscanf.c
-$(OBJDIR)/vsscanf.o: src/stdio/_stdio.h
+$(OBJDIR)/vsscanf.o: src/stdio/_format.h
 $(OBJDIR)/vsscanf.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vsscanf.c
diff --git a/mk/vsscanf_s.d b/mk/vsscanf_s.d
index 1a9e2436..6cd54265 100644
--- a/mk/vsscanf_s.d
+++ b/mk/vsscanf_s.d
@@ -3,7 +3,7 @@ libc.a(vsscanf_s.o): $(OBJDIR)/vsscanf_s.o
 	@$(AR) $(ARFLAGS) $@ $(OBJDIR)/$%
 
 $(OBJDIR)/vsscanf_s.o: src/stdio/vsscanf_s.c
-$(OBJDIR)/vsscanf_s.o: src/stdio/_stdio.h
+$(OBJDIR)/vsscanf_s.o: src/stdio/_format.h
 $(OBJDIR)/vsscanf_s.o:
 	@mkdir -p $(@D)
 	$(CC) -c -o $@ $(CFLAGS) src/stdio/vsscanf_s.c
diff --git a/src/stdio/__conv.c b/src/stdio/__conv.c
index 994bb072..2b317400 100644
--- a/src/stdio/__conv.c
+++ b/src/stdio/__conv.c
@@ -1,7 +1,7 @@
 #include <inttypes.h>
 #include <ctype.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 static char *length_names[] = {
 	[L_hh] = "hh",
@@ -39,7 +39,7 @@ size_t __conv(const char *format, struct io_conversion *conv, va_list arg)
 
 		if (conv->dir == IO_IN) {
 			if ((conv->flags & ~(F_STAR)) != 0) {
-				UNDEFINED("Flag '%c' is not valid for formatted input", format[ret]);
+				UNDEFINED_FMT(conv, "Flag '%c' is not valid for formatted input", format[ret]);
 			}
 		} else {
 			if (conv->flags & F_STAR) {
@@ -101,7 +101,7 @@ size_t __conv(const char *format, struct io_conversion *conv, va_list arg)
 	case 'd':
 	case 'i':
 		if (conv->length == L_L) {
-			UNDEFINED("In call to %s(): Length '%s' is not supported with conversion specifier '%c'", conv->func, length_names[conv->length], conv->spec);
+			UNDEFINED_FMT(conv, "Length '%s' is not supported with conversion specifier '%c'", length_names[conv->length], conv->spec);
 		}
 		break;
 
@@ -110,7 +110,7 @@ size_t __conv(const char *format, struct io_conversion *conv, va_list arg)
 	case 'x':
 	case 'X':
 		if (conv->length == L_L) {
-			UNDEFINED("In call to %s(): Length '%s' is not supported with conversion specifier '%c'", conv->func, length_names[conv->length], conv->spec);
+			UNDEFINED_FMT(conv, "Length '%s' is not supported with conversion specifier '%c'", length_names[conv->length], conv->spec);
 		}
 		break;
 
@@ -123,20 +123,20 @@ size_t __conv(const char *format, struct io_conversion *conv, va_list arg)
 	case 'a':
 	case 'A':
 		if (conv->length != L_L && conv->length) {
-			UNDEFINED("In call to %s(): Length '%s' is not supported with conversion specifier '%c'", conv->func, length_names[conv->length], conv->spec);
+			UNDEFINED_FMT(conv, "Length '%s' is not supported with conversion specifier '%c'", length_names[conv->length], conv->spec);
 		}
 		break;
 
 	case 'c':
 		if (conv->flags & F_PRECISION) {
-			UNDEFINED("In call to %s(): Precision is not supported with conversion specifier '%c'", conv->func, conv->spec);
+			UNDEFINED_FMT(conv, "Precision is not supported with conversion specifier '%c'", conv->spec);
 		}
 		/* FALLTHRU */
 
 	case 's':
 	case '[':
 		if (conv->length != L_l && conv->length) {
-			UNDEFINED("In call to %s(): Length '%s' is not supported with conversion specifier '%c'", conv->func, length_names[conv->length], conv->spec);
+			UNDEFINED_FMT(conv, "Length '%s' is not supported with conversion specifier '%c'", length_names[conv->length], conv->spec);
 		}
 		break;
 
@@ -144,21 +144,21 @@ size_t __conv(const char *format, struct io_conversion *conv, va_list arg)
 	case 'n':
 	case '%':
 		if (conv->flags & F_WIDTH) {
-			UNDEFINED("In call to %s(): Field width is not supported with conversion specififier '%c'", conv->func, conv->spec);
+			UNDEFINED_FMT(conv, "Field width is not supported with conversion specififier '%c'", conv->spec);
 		}
 		if (conv->flags & F_PRECISION) {
-			UNDEFINED("In call to %s(): Precision is not supported with conversion specififier '%c'", conv->func, conv->spec);
+			UNDEFINED_FMT(conv, "Precision is not supported with conversion specififier '%c'", conv->spec);
 		}
 		if (conv->flags) {
-			UNDEFINED("In call to %s(): Flags are not supported with conversion specifier '%c'", conv->func, conv->spec);
+			UNDEFINED_FMT(conv, "Flags are not supported with conversion specifier '%c'", conv->spec);
 		}
 		if (conv->length) {
-			UNDEFINED("In call to %s(): Length '%s' is not supported with conversion specifier '%c'", conv->func, length_names[conv->length], conv->spec);
+			UNDEFINED_FMT(conv, "Length '%s' is not supported with conversion specifier '%c'", length_names[conv->length], conv->spec);
 		}
 		break;
 
 	default:
-		UNDEFINED("In call to %s(): Unknown conversion specifier '%c'", conv->func, conv->spec);
+		UNDEFINED_FMT(conv, "Unknown conversion specifier '%c'", conv->spec);
 	}
 
 	return ret;
diff --git a/src/stdio/__printf.c b/src/stdio/__printf.c
index d0672d14..3471db74 100644
--- a/src/stdio/__printf.c
+++ b/src/stdio/__printf.c
@@ -10,7 +10,7 @@
 #endif
 
 #include "_forced/strdup.h"
-#include "_stdio.h"
+#include "_format.h"
 
 #define NUMBUFLEN 64
 
@@ -129,6 +129,7 @@ int __printf(struct io_options *opt, const char * format, va_list arg)
 		struct io_conversion conv = {
 			.func = opt->fnname,
 			.dir = IO_OUT,
+			.fmt = format,
 		};
 		int base = 10;
 
diff --git a/src/stdio/__scanf.c b/src/stdio/__scanf.c
index 5e43303e..f39fdfc0 100644
--- a/src/stdio/__scanf.c
+++ b/src/stdio/__scanf.c
@@ -5,7 +5,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 #include "_safety.h"
 
 #pragma GCC diagnostic ignored "-Wint-conversion"
@@ -129,6 +129,7 @@ int __scanf(struct io_options *opt, const char * format, va_list arg)
 		struct io_conversion conv = {
 			.func = opt->fnname,
 			.dir = IO_IN,
+			.fmt = format,
 		};
 
 		if (isspace(*format)) {
diff --git a/src/stdio/_format.h b/src/stdio/_format.h
new file mode 100644
index 00000000..5930fdb6
--- /dev/null
+++ b/src/stdio/_format.h
@@ -0,0 +1,82 @@
+#ifndef __STDIO__FORMAT_H__
+#define __STDIO__FORMAT_H__
+
+#include <inttypes.h>
+#include <stddef.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include "_stdio.h"
+#include "_safety.h"
+
+#define UNDEFINED_FMT(__conv, __fmt, ...) do { \
+	char __buf[128]; \
+	snprintf(__buf, sizeof(__buf), "In call to %s() with format string \"%s\": Invalid conversion specification: ", __conv->func, __conv->fmt); \
+	__undefined("%s" __fmt, __buf, __VA_ARGS__); \
+} while (0)
+
+struct io_options {
+	const char *fnname;	/* the calling function */
+	char *string;		/* NULL or the output string */
+	wchar_t *wstring;	/* NULL or the output wide string */
+	FILE *stream;		/* NULL or the output stream */
+	int fd;			/* -1 or the output file descriptor */
+	size_t maxlen;		/* max number of bytes to write to string */
+	size_t pos;		/* current index in string */
+	int ret;		/* return value */
+};
+
+struct io_conversion {
+	const char *func;
+	const char *fmt;
+	enum { IO_IN, IO_OUT } dir;
+	enum conversion_flags {
+		/* explicit */
+		F_STAR = (1<<0),
+		F_LEFT = (1<<1),
+		F_SIGN = (1<<2),
+		F_SPACE = (1<<3),
+		F_ALT = (1<<4),
+		F_ZERO = (1<<5),
+
+		/* inferred */
+		F_UPPER = (1<<10),
+		F_WIDTH = (1<<11),
+		F_PRECISION = (1<<12),
+	} flags;
+	enum conversion_length {
+		L_default,
+		L_hh,
+		L_ll,
+		L_h,
+		L_l,
+		L_j,
+		L_z,
+		L_t,
+		L_L,
+	} length;
+	uintmax_t width;
+	uintmax_t precision;
+	char spec;
+	union {
+		uintmax_t u;
+		intmax_t i;
+		float f;
+		double d;
+		long double ld;
+		char *s;
+		wchar_t *wcs;
+		char c;
+		wchar_t wc;
+		void *ptr;
+	} val;
+};
+
+size_t __conv(const char *, struct io_conversion *, va_list);
+int __printf(struct io_options * restrict, const char * restrict, va_list);
+int __scanf(struct io_options * restrict, const char * restrict, va_list);
+
+/*
+STDC(-1)
+*/
+
+#endif
diff --git a/src/stdio/_stdio.h b/src/stdio/_stdio.h
index 1894e956..8cbf453c 100644
--- a/src/stdio/_stdio.h
+++ b/src/stdio/_stdio.h
@@ -46,6 +46,13 @@
 			UNDEFINED("In call to %s(): Requested %s operation on %s oriented stream", __func__, (__orientation) > 0 ? "wide" : "byte", ((__stream)->orientation) > 0 ? "wide" : "byte"); \
 		} \
 	} while (0)
+
+#define ASSERT_FPOS(__stream, __pos) do { \
+	if (!(__pos->__impl >= __stream->fpos && __pos->__impl <= __stream->fpos + __stream->nfpos)) { \
+		UNDEFINED("In call to %s(): %s must be previously set by calling fesetpos()", __func__, #__pos); \
+	} \
+} while (0)
+
 #endif
 
 struct __FILE {
@@ -79,72 +86,16 @@ struct __FILE {
 	pid_t pipe_pid;		/* if stream is a pipe, the child pid */
 	#endif
 
-	fpos_t *valid_fpos;
-	size_t nvalid_fpos;
+	struct __fpos_t *fpos;
+	size_t nfpos;
 	long int *valid_ftell;
 	size_t nvalid_ftell;
 };
 
-struct io_options {
-	const char *fnname;	/* the calling function */
-	char *string;		/* NULL or the output string */
-	wchar_t *wstring;	/* NULL or the output wide string */
-	FILE *stream;		/* NULL or the output stream */
-	int fd;			/* -1 or the output file descriptor */
-	size_t maxlen;		/* max number of bytes to write to string */
-	size_t pos;		/* current index in string */
-	int ret;		/* return value */
+struct __fpos_t {
+	size_t pos;
 };
 
-struct io_conversion {
-	const char *func;
-	enum { IO_IN, IO_OUT } dir;
-	enum conversion_flags {
-		/* explicit */
-		F_STAR = (1<<0),
-		F_LEFT = (1<<1),
-		F_SIGN = (1<<2),
-		F_SPACE = (1<<3),
-		F_ALT = (1<<4),
-		F_ZERO = (1<<5),
-
-		/* inferred */
-		F_UPPER = (1<<10),
-		F_WIDTH = (1<<11),
-		F_PRECISION = (1<<12),
-	} flags;
-	enum conversion_length {
-		L_default,
-		L_hh,
-		L_ll,
-		L_h,
-		L_l,
-		L_j,
-		L_z,
-		L_t,
-		L_L,
-	} length;
-	uintmax_t width;
-	uintmax_t precision;
-	char spec;
-	union {
-		uintmax_t u;
-		intmax_t i;
-		float f;
-		double d;
-		long double ld;
-		char *s;
-		wchar_t *wcs;
-		char c;
-		wchar_t wc;
-		void *ptr;
-	} val;
-};
-
-size_t __conv(const char *, struct io_conversion *, va_list);
-int __printf(struct io_options * restrict, const char * restrict, va_list);
-int __scanf(struct io_options * restrict, const char * restrict, va_list);
-
 extern struct __stdio_h {
 	struct __FILE FILES[FOPEN_MAX];
 	char **formatted_pointers;
diff --git a/src/stdio/fgetpos.c b/src/stdio/fgetpos.c
index 8e6d201e..2f105f6a 100644
--- a/src/stdio/fgetpos.c
+++ b/src/stdio/fgetpos.c
@@ -6,10 +6,21 @@
 int fgetpos(FILE * restrict stream, fpos_t * restrict pos)
 {
 	SIGNAL_SAFE(0);
+	ASSERT_STREAM(stream, 0, 0);
+	ASSERT_NONNULL(pos);
 	ASSERT_NOOVERLAP(stream, sizeof(*stream), pos, sizeof(*pos));
 
 	flockfile(stream);
-	*pos = stream->pos;
+	if (!(pos->__impl >= stream->fpos && pos->__impl <= stream->fpos + stream->nfpos)) {
+		struct __fpos_t *tmp = realloc(stream->fpos, sizeof(*stream->fpos) * (stream->nfpos + 1));
+		if (tmp == NULL) {
+			abort();
+		}
+		stream->fpos = tmp;
+		pos->__impl = &(stream->fpos[stream->nfpos++]);
+	}
+
+	pos->__impl->pos = ftell(stream);
 	funlockfile(stream);
 	return 0;
 }
diff --git a/src/stdio/fprintf.c b/src/stdio/fprintf.c
index bab6455a..c773a72a 100644
--- a/src/stdio/fprintf.c
+++ b/src/stdio/fprintf.c
@@ -1,7 +1,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a file stream **/
 
diff --git a/src/stdio/fprintf_s.c b/src/stdio/fprintf_s.c
index 83843f78..8fc38f9f 100644
--- a/src/stdio/fprintf_s.c
+++ b/src/stdio/fprintf_s.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a file stream **/
 int fprintf_s(FILE * restrict stream, const char * restrict format, ...)
diff --git a/src/stdio/freopen.c b/src/stdio/freopen.c
index 60394ca6..941ffb9b 100644
--- a/src/stdio/freopen.c
+++ b/src/stdio/freopen.c
@@ -82,8 +82,8 @@ FILE * freopen(const char * restrict filename, const char * restrict mode, FILE
 		stream->buf = stream->ibuf;
 	}
 
-	free(stream->valid_fpos);
-	stream->nvalid_fpos = 0;
+	free(stream->fpos);
+	stream->nfpos = 0;
 
 	free(stream->valid_ftell);
 	stream->nvalid_ftell = 0;
diff --git a/src/stdio/fscanf.c b/src/stdio/fscanf.c
index 2299fd11..718cd0d4 100644
--- a/src/stdio/fscanf.c
+++ b/src/stdio/fscanf.c
@@ -1,7 +1,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** read formatted input from a file stream **/
 
diff --git a/src/stdio/fscanf_s.c b/src/stdio/fscanf_s.c
index 310ca5da..a82c45ec 100644
--- a/src/stdio/fscanf_s.c
+++ b/src/stdio/fscanf_s.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** read formatted input from a file stream **/
 int fscanf_s(FILE * restrict stream, const char * restrict format, ...)
diff --git a/src/stdio/fsetpos.c b/src/stdio/fsetpos.c
index c75fed41..f4aaf71c 100644
--- a/src/stdio/fsetpos.c
+++ b/src/stdio/fsetpos.c
@@ -6,6 +6,8 @@
 int fsetpos(FILE *stream, const fpos_t *pos)
 {
 	SIGNAL_SAFE(0);
+	ASSERT_STREAM(stream, 0, 0);
+	ASSERT_FPOS(stream, pos);
 	ASSERT_NOOVERLAP(stream, sizeof(*stream), pos, sizeof(*pos));
 
 	(void)stream; (void)pos;
diff --git a/src/stdio/printf.c b/src/stdio/printf.c
index 03b6df2a..793462ff 100644
--- a/src/stdio/printf.c
+++ b/src/stdio/printf.c
@@ -1,6 +1,6 @@
 #include <stdarg.h>
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output **/
 
diff --git a/src/stdio/printf_s.c b/src/stdio/printf_s.c
index 92b4ca7c..3ba50642 100644
--- a/src/stdio/printf_s.c
+++ b/src/stdio/printf_s.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <stdarg.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output **/
 int printf_s(const char *format, ...)
diff --git a/src/stdio/scanf.c b/src/stdio/scanf.c
index d7de9a7c..49935f1a 100644
--- a/src/stdio/scanf.c
+++ b/src/stdio/scanf.c
@@ -1,6 +1,6 @@
 #include <stdarg.h>
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** read formatted input **/
 
diff --git a/src/stdio/scanf_s.c b/src/stdio/scanf_s.c
index d4618cd7..add9f703 100644
--- a/src/stdio/scanf_s.c
+++ b/src/stdio/scanf_s.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <stdarg.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** read formatted input **/
 int scanf_s(const char * restrict format, ...)
diff --git a/src/stdio/snprintf.c b/src/stdio/snprintf.c
index c77239c4..05d22c95 100644
--- a/src/stdio/snprintf.c
+++ b/src/stdio/snprintf.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 GCC_SSE_HACK
 int snprintf(char * restrict s, size_t n, const char * restrict format, ...)
diff --git a/src/stdio/snprintf_s.c b/src/stdio/snprintf_s.c
index b3b8c0fc..6f6ac1df 100644
--- a/src/stdio/snprintf_s.c
+++ b/src/stdio/snprintf_s.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int snprintf_s( char * restrict s, rsize_t n, const char * restrict format, ...)
 {
diff --git a/src/stdio/sprintf.c b/src/stdio/sprintf.c
index fcb1ddac..3b815ab7 100644
--- a/src/stdio/sprintf.c
+++ b/src/stdio/sprintf.c
@@ -1,6 +1,6 @@
 #include <stdarg.h>
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a string **/
 
diff --git a/src/stdio/sprintf_s.c b/src/stdio/sprintf_s.c
index e640abf7..e2914e13 100644
--- a/src/stdio/sprintf_s.c
+++ b/src/stdio/sprintf_s.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a string **/
 int sprintf_s(char * restrict s, rsize_t n, const char * restrict format, ...)
diff --git a/src/stdio/sscanf.c b/src/stdio/sscanf.c
index 4fab8b61..c9f1c1f6 100644
--- a/src/stdio/sscanf.c
+++ b/src/stdio/sscanf.c
@@ -1,7 +1,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** read formatted input from a string **/
 
diff --git a/src/stdio/sscanf_s.c b/src/stdio/sscanf_s.c
index 08bbd6e5..159b2893 100644
--- a/src/stdio/sscanf_s.c
+++ b/src/stdio/sscanf_s.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** read formatted input from a string **/
 int sscanf_s(const char * restrict s, const char * restrict format, ...)
diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index 958e04fe..5cfb3afa 100644
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -1,7 +1,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a file stream **/
 
diff --git a/src/stdio/vfprintf_s.c b/src/stdio/vfprintf_s.c
index b11f27e8..434f5cf5 100644
--- a/src/stdio/vfprintf_s.c
+++ b/src/stdio/vfprintf_s.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a file stream **/
 int vfprintf_s(FILE * restrict stream, const char * restrict format, va_list arg)
diff --git a/src/stdio/vfscanf.c b/src/stdio/vfscanf.c
index af0dc289..79694ab9 100644
--- a/src/stdio/vfscanf.c
+++ b/src/stdio/vfscanf.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vfscanf(FILE * restrict stream, const char * restrict format, va_list arg)
 {
diff --git a/src/stdio/vfscanf_s.c b/src/stdio/vfscanf_s.c
index 7654abd3..47add45c 100644
--- a/src/stdio/vfscanf_s.c
+++ b/src/stdio/vfscanf_s.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vfscanf_s(FILE * restrict stream, const char * restrict format, va_list arg)
 {
diff --git a/src/stdio/vprintf.c b/src/stdio/vprintf.c
index 00c21419..8db52891 100644
--- a/src/stdio/vprintf.c
+++ b/src/stdio/vprintf.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <stdarg.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output **/
 int vprintf(const char * restrict format, va_list arg)
diff --git a/src/stdio/vprintf_s.c b/src/stdio/vprintf_s.c
index 5f462e7e..b08b6da6 100644
--- a/src/stdio/vprintf_s.c
+++ b/src/stdio/vprintf_s.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output **/
 int vprintf_s(const char * restrict format, va_list arg)
diff --git a/src/stdio/vscanf.c b/src/stdio/vscanf.c
index 701ac478..2b94b61c 100644
--- a/src/stdio/vscanf.c
+++ b/src/stdio/vscanf.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vscanf(const char * restrict format, va_list arg)
 {
diff --git a/src/stdio/vscanf_s.c b/src/stdio/vscanf_s.c
index d8bf0418..9c96df0f 100644
--- a/src/stdio/vscanf_s.c
+++ b/src/stdio/vscanf_s.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vscanf_s(const char * restrict format, va_list arg)
 {
diff --git a/src/stdio/vsnprintf.c b/src/stdio/vsnprintf.c
index 87deb169..373ab5a0 100644
--- a/src/stdio/vsnprintf.c
+++ b/src/stdio/vsnprintf.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vsnprintf(char * restrict s, size_t n, const char *format, va_list arg)
 {
diff --git a/src/stdio/vsnprintf_s.c b/src/stdio/vsnprintf_s.c
index 2f980931..e302a19c 100644
--- a/src/stdio/vsnprintf_s.c
+++ b/src/stdio/vsnprintf_s.c
@@ -1,6 +1,6 @@
 #include <stdio.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vsnprintf_s(char * restrict s, rsize_t n, const char * restrict format, va_list arg)
 {
diff --git a/src/stdio/vsprintf.c b/src/stdio/vsprintf.c
index 6edf9f2f..c218a3da 100644
--- a/src/stdio/vsprintf.c
+++ b/src/stdio/vsprintf.c
@@ -1,6 +1,6 @@
 #include <stdarg.h>
 #include <stdio.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a string **/
 
diff --git a/src/stdio/vsprintf_s.c b/src/stdio/vsprintf_s.c
index 38500801..7e226765 100644
--- a/src/stdio/vsprintf_s.c
+++ b/src/stdio/vsprintf_s.c
@@ -2,7 +2,7 @@
 #include <stdarg.h>
 #include <stdint.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 /** write formatted output to a string **/
 int vsprintf_s(char *s, rsize_t n, const char *format, va_list arg)
diff --git a/src/stdio/vsscanf.c b/src/stdio/vsscanf.c
index 183d9f2d..5113c34e 100644
--- a/src/stdio/vsscanf.c
+++ b/src/stdio/vsscanf.c
@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vsscanf(const char * restrict s, const char * restrict format, va_list arg)
 {
diff --git a/src/stdio/vsscanf_s.c b/src/stdio/vsscanf_s.c
index 63ec80bf..f5a0a31b 100644
--- a/src/stdio/vsscanf_s.c
+++ b/src/stdio/vsscanf_s.c
@@ -1,6 +1,6 @@
 #include <stdarg.h>
 #include <string.h>
-#include "_stdio.h"
+#include "_format.h"
 
 int vsscanf_s(const char * restrict s, const char * restrict format, va_list arg)
 {