1 files changed, 21 insertions, 0 deletions
diff --git a/userland/libc/string/strstr.c b/userland/libc/string/strstr.c
new file mode 100644
index 0000000..20b9dc2
--- /dev/null
+++ b/userland/libc/string/strstr.c
@@ -0,0 +1,21 @@
+#include <string.h>
+
+char *strstr(const char *s1, const char *s2) {
+  // If s2 points to a string with zero length, the function shall return s1.
+  if ('\0' == *s2)
+    return s1;
+  for (; *s1; s1++) {
+    const char *t1 = s1;
+    const char *t2 = s2;
+    int is_dif = 0;
+    for (; *t2 && *t1; t1++, t2++) {
+      if (*t2 != *t1) {
+        is_dif = 1;
+        break;
+      }
+    }
+    if (!is_dif)
+      return s1;
+  }
+  return NULL;
+}