const correctness in C

const on a parameter is a promise to the caller, and the compiler enforces it.

size_t count_char(const char *text, char target) {
    size_t found = 0;
    while (*text != '\0') {
        if (*text == target) {
            found++;
        }
        text++;
    }
    return found;
}

void demonstrate(void) {
    char buffer[] = "mississippi";
    const char *reader = buffer;
    char *const fixed = buffer;

    *fixed = 'M';
    (void) reader;
    (void) count_char(buffer, 's');
}

How it works

1. const char *p may not write through p.
2. char *const p may not point somewhere else.
3. Taking const where you can read is the polite signature.

Keywords and builtins used here

• char
• const
• count_char
• demonstrate
• if
• return
• size_t
• void
• while

The run, in numbers

Lines

20

Characters to type

330

Tokens

105

Three-star pace

90 tpm

At the three-star pace of 90 tokens a minute, this run takes about 70 seconds.

Type this snippet

Step 2 of 4 in Values & storage, step 28 of 35 in Language basics.

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