1 files changed, 43 insertions, 0 deletions
diff --git a/src/string/strstr.c b/src/string/strstr.c
new file mode 100644
index 00000000..898db1be
--- /dev/null
+++ b/src/string/strstr.c
@@ -0,0 +1,43 @@
+#include <string.h>
+#include "nonstd/assert.h"
+
+/** search for substring **/
+char * strstr(const char *s1, const char *s2)
+{
+	size_t l1 = 0;
+	size_t l2 = 0;
+	char *p = (char*)s1;
+
+	ASSERT_NONNULL(s1);
+	ASSERT_NONNULL(s2);
+
+	l2 = strlen(s2);
+	if (l2 == 0) {
+		return p;
+	}
+
+	l1 = strlen(s1);
+	
+	do {
+		p = memchr(p, *s2, l1);
+		if (p == NULL || strcmp(p + 1, s2 + 1) == 0) {
+			break;
+		}
+		p++;
+	} while (p < s1 + l2);
+
+	/*
+	RETURN_FAILURE(CONSTANT(NULL));
+	RETURN_SUCCESS(a pointer to the located string);
+	*/
+	return p;
+}
+
+/***
+finds the first occurrence of the string ARGUMENT(s2) in the string
+ARGUMENT(s1). Specifying the empty string for ARGUMENT(s2) matches the first
+character of ARGUMENT(s1).
+***/
+/*
+STDC(1)
+*/