Case conversion and comparison in C

Converting in place, and comparing without regard to case.

void upper_in_place(char *text) {
    for (; *text; text++) {
        *text = (char) toupper((unsigned char) *text);
    }
}

int ci_compare(const char *a, const char *b) {
    while (*a && *b) {
        int x = tolower((unsigned char) *a);
        int y = tolower((unsigned char) *b);
        if (x != y) {
            return (x > y) - (x < y);
        }
        a++;
        b++;
    }
    return (*a != '\0') - (*b != '\0');
}

How it works

1. toupper takes and returns an int, so cast on the way in and out.
2. There is no portable case-insensitive strcmp in ISO C.
3. Writing one is four lines, and it is exactly this.

Keywords and builtins used here

• char
• ci_compare
• const
• for
• if
• int
• return
• unsigned
• upper_in_place
• void
• while

The run, in numbers

Lines

18

Characters to type

341

Tokens

140

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 84 seconds.

Type this snippet

Step 1 of 2 in Transforming, step 11 of 13 in Strings & text.

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