Add tests and fix code

src/string.c

@@ -67,8 +67,12 @@ char *LIBCLAYER(strchr)(const char *s, int c)
 
 int LIBCLAYER(strcmp)(const char *s1, const char *s2)
 {
-    for (; *s1; ++s1, ++s2) if (*s1 != *s2) return *s1 < *s2 ? -1 : 1;
+    for (;;) {
-    return 0;
+        const char c1 = *s1++;
+        const char c2 = *s2++;
+        if (c1 != c2) return c1 < c2 ? -1 : 1;
+        if (!c1) return 0;
+    }
 }
 
 char *LIBCLAYER(strcpy)(char *dest, const char *src)

tests/string.c

@@ -13,6 +13,12 @@ static char aaa[COUNT], bbb[COUNT];
 #define memchr  LIBCLAYER(memchr)
 #define memset  LIBCLAYER(memset)
 
+#define strcat  LIBCLAYER(strcat)
+#define strchr  LIBCLAYER(strchr)
+#define strcmp  LIBCLAYER(strcmp)
+#define strcpy  LIBCLAYER(strcpy)
+#define strlen  LIBCLAYER(strlen)
+
 void test_main()
 {
     { // memcmp
@@ -50,4 +56,45 @@ void test_main()
         for (size_t i = 0;         i < COUNT / 2; ++i) assert(aaa[i] == 'a');
         for (size_t i = COUNT / 2; i < COUNT;     ++i) assert(aaa[i] == 'b');
     }
+
+    { // strcat
+        aaa[0] = 'f'; aaa[1] = 'o'; aaa[2] = 'o'; aaa[3] = '\0';
+        strcat(aaa, "bar");
+        for (const char *e = "foobar", *g = aaa; *e; ++e, ++g) assert(*g == *e);
+        assert(aaa[6] == '\0');
+    }
+
+    { // strchr
+        const char *const s = "foobar";
+        assert(strchr(s, 'f') == &s[0]);
+        assert(strchr(s, 'b') == &s[3]);
+        assert(strchr(s, 'r') == &s[5]);
+        assert(strchr(s, 'x') == NULL);
+        assert(strchr(s, 'F') == NULL);
+    }
+
+    { // strcmp
+        assert(strcmp("", "") == 0);
+        assert(strcmp("", "a") == -1);
+        assert(strcmp("a", "") == 1);
+        assert(strcmp("a", "a") == 0);
+        assert(strcmp("a", "aa") == -1);
+        assert(strcmp("aa", "a") == 1);
+        assert(strcmp("aa", "ab") == -1);
+        assert(strcmp("ab", "aa") == 1);
+        assert(strcmp("aa", "aa") == 0);
+    }
+
+    { // strcpy
+        assert(strcpy(aaa, "foobar") == aaa);
+        for (const char *e = "foobar", *g = aaa; *e; ++e, ++g) assert(*g == *e);
+        assert(aaa[6] == '\0');
+    }
+
+    { // strlen
+        assert(strlen("") == 0);
+        assert(strlen("a") == 1);
+        assert(strlen("aa") == 2);
+        assert(strlen("aaaaaaaaaa") == 10);
+    }
 }