StrStartsWith

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API Reference

StrStartsWith

Description

Check whether a Str starts with a prefix.

Three call shapes via OVERLOAD + _Generic on prefix: StrStartsWith(s, prefix) – prefix is Str * or Zstr. StrStartsWith(s, prefix, prefix_len) – prefix is a fixed-length view (Zstr, size).

Parameters

Name	Direction	Description
`s`	in	Str to check.
`prefix`	in	Candidate prefix (`Str *` / `Zstr`).
`prefix_len`	in	Length of `prefix` when using the 3-arg fixed-length form.

Success

Returns true when s starts with prefix. The string is not modified.

Failure

Returns false. The string is not modified.

Usage example (Cross-references)

Usage examples (Cross-references)

In Ops.c:126:

    // Test string starts/ends with functions
    bool test_str_starts_ends_with(void) {
        WriteFmt("Testing StrStartsWith and StrEndsWith variants\n");
        DefaultAllocator alloc = DefaultAllocatorInit();

In Ops.c:135:

    
        // Test Str-form
        bool result = StrStartsWith(&s, &prefix);
    
        // Test Str-form

In Ops.c:141:

    
        // Test Zstr-form (string literal)
        result = result && StrStartsWith(&s, "Hello");
        result = result && !StrStartsWith(&s, "World");

In Ops.c:142:

        // Test Zstr-form (string literal)
        result = result && StrStartsWith(&s, "Hello");
        result = result && !StrStartsWith(&s, "World");
    
        // Test Zstr-form (string literal)

In Ops.c:149:

    
        // Test Cstr-form (fixed-length view)
        result = result && StrStartsWith(&s, "Hell", 4);
        result = result && !StrStartsWith(&s, "Worl", 4);

In Ops.c:150:

        // Test Cstr-form (fixed-length view)
        result = result && StrStartsWith(&s, "Hell", 4);
        result = result && !StrStartsWith(&s, "Worl", 4);
    
        // Test Cstr-form (fixed-length view)

In Ops.c:592:

    // mutant rejects it outright.
    static bool test_starts_with_full_string(void) {
        WriteFmt("Testing StrStartsWith with a prefix equal to the whole string\n");
        DefaultAllocator alloc = DefaultAllocatorInit();

In Ops.c:597:

        Str s = StrInitFromZstr("Hello", &alloc);
    
        bool result = (StrStartsWith(&s, "Hello") == true);
        if (!result) {
            WriteFmt("    FAIL: Expected StrStartsWith true for full-string prefix\n");

In Ops.c:599:

        bool result = (StrStartsWith(&s, "Hello") == true);
        if (!result) {
            WriteFmt("    FAIL: Expected StrStartsWith true for full-string prefix\n");
        }

In Ops.c:654:

    //   mutant : always false.
    static bool test_starts_with_true_on_match(void) {
        WriteFmt("Testing StrStartsWith returns true on a real prefix match (466:12)\n");
        DefaultAllocator alloc = DefaultAllocatorInit();

In Ops.c:660:

        Str prefix = StrInitFromZstr("Hello", &alloc);
    
        bool result = (StrStartsWith(&s, &prefix) == true);
        if (!result) {
            WriteFmt("    FAIL: expected true for prefix 'Hello'\n");

In Ops.c:916:

    // (Str.Mutants6).
    static bool test_starts_with_cstr_null_aborts(void) {
        WriteFmt("Testing StrStartsWith(Cstr) aborts on NULL Str\n");
    
        (void)StrStartsWith((Str *)NULL, "x", (size)1);

In Ops.c:918:

        WriteFmt("Testing StrStartsWith(Cstr) aborts on NULL Str\n");
    
        (void)StrStartsWith((Str *)NULL, "x", (size)1);
    
        return false;

In Ops.c:1089:

        s.__magic  = 0;
    
        (void)StrStartsWith(&s, &prefix);
    
        StrDeinit(&prefix);

Last updated on July 1, 2026

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