strings.c: enforce null-termination on strncpy, optimize strcat

F/439
F/440

Author: danielinux

src/string.c

@@ -98,8 +98,9 @@ char *strcat(char *dest, const char *src)
 {
     size_t i = 0;
     size_t j = strlen(dest);
+    size_t src_len = strlen(src);
 
-    for (i = 0; i < strlen(src); i++) {
+    for (i = 0; i < src_len; i++) {
         dest[j++] = src[i];
     }
     dest[j] = '\0';
@@ -186,6 +187,10 @@ char *strncpy(char *dst, const char *src, size_t n)
             break;
     }
 
+    while (++i < n) {
+        dst[i] = '\0';
+    }
+
     return dst;
 }
 

tools/unit-tests/unit-string.c

@@ -237,6 +237,7 @@ START_TEST(test_strcpy_strncpy_strcat_strncat)
     char buf[8];
     char dest[8];
     char short_dest[4];
+    char padded[8];
 
     strcpy(buf, "hi");
     ck_assert_str_eq(buf, "hi");
@@ -245,6 +246,17 @@ START_TEST(test_strcpy_strncpy_strcat_strncat)
     strncpy(dest, "abc", 4);
     ck_assert_str_eq(dest, "abc");
 
+    memset(padded, 'X', sizeof(padded));
+    strncpy(padded, "abc", sizeof(padded));
+    ck_assert_int_eq(padded[0], 'a');
+    ck_assert_int_eq(padded[1], 'b');
+    ck_assert_int_eq(padded[2], 'c');
+    ck_assert_int_eq(padded[3], '\0');
+    ck_assert_int_eq(padded[4], '\0');
+    ck_assert_int_eq(padded[5], '\0');
+    ck_assert_int_eq(padded[6], '\0');
+    ck_assert_int_eq(padded[7], '\0');
+
     memset(short_dest, 'X', sizeof(short_dest));
     strncpy(short_dest, "abcdef", 3);
     ck_assert_int_eq(short_dest[0], 'a');