Remove leading/trailing spaces without isspace()

Question

I was looking for a standard way to remove leading spaces, and I found a pretty simple way using pointers and isspace(), however our professor won't allow us to use the <ctype.h> library. Would the following work?

char LeadingSpace(char *line) {
    while (line[0] == ' ') {
        line++;
    }
    return line;
}

I'm new to C so not entirely sure how pointers work, but if I move the pointer everytime I find a leading space, then I would only have to check line[0], right?

Yes this code would do what you want, however, if `line` was allocated using `malloc()` you cannot use the returned pointer for `free()`. Also, it seems that you missed a `*` in the function definition. And finally, you should be aware that `isspace()` not only ignores `' '` but `'\t'`, `'\n'` and `'\r'` too. — Iharob Al Asimi, Dec 12 '15 at 18:51
@iharob Alright, thanks so much! Learned a lot just from that. — Quinn Tai, Dec 12 '15 at 18:55

score 1 · Answer 1 · answered Dec 12 '15 at 19:03

1

Yes - Checking line[0] == ' ' is fine:

But this line

char LeadingSpace(char *line) {

should be

char* LeadingSpace(char *line) {

As you are returning a character pointer

answered Dec 12 '15 at 19:03

Ed Heal

59,252
17
87
127

I have a doubt. In the question is he returning a character? – Cherubim Dec 12 '15 at 19:10
Please re-read - the type of line is `char *` - the bit I corrected – Ed Heal Dec 12 '15 at 19:11

score 0 · Answer 2 · answered Dec 12 '15 at 19:10

0

try this

char* LeadingSpace(char *line) {
    while (line[0] == ' ' || line[0] == '\t' || line[0] == '\n' || line[0] == '\r') {
        line++;
    }
    return line;
}

or this using string.h header

char* LeadingSpace(char *line) {
    while (strchr(" \t\r\n", line[0])) {
        line++;
    }
    return line;
}

answered Dec 12 '15 at 19:10

Luis Daniel

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7
18

Note that using a switch would be clearer. The `strchr()` trick is very nice. – Iharob Al Asimi Dec 12 '15 at 19:29

Remove leading/trailing spaces without isspace()

2 Answers2