Trimming whitespace in C

Trimming in place: walk forward for the start, backward for the end.

char *trim(char *text) {
    while (isspace((unsigned char) *text)) {
        text++;
    }
    char *end = text + strlen(text);
    while (end > text && isspace((unsigned char) end[-1])) {
        end--;
    }
    *end = '\0';
    return text;
}

int is_blank(const char *text) {
    for (; *text; text++) {
        if (!isspace((unsigned char) *text)) {
            return 0;
        }
    }
    return 1;
}

How it works

1. Leading space is skipped by advancing a pointer.
2. Trailing space is removed by writing an earlier NUL.
3. Returning the new start avoids copying anything.

Keywords and builtins used here

• char
• const
• for
• if
• int
• is_blank
• return
• trim
• unsigned
• while

The run, in numbers

Lines

20

Characters to type

325

Tokens

117

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 70 seconds.

Type this snippet

Step 3 of 3 in Splitting & parsing, step 10 of 13 in Strings & text.

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