How to remove \n or \t from a given string in C?

Question

How can I strip a string with all \n and \t in C?

Answer 1

This works in my quick and dirty tests. Does it in place:

#include <stdio.h>

void strip(char *s) {
    char *p2 = s;
    while(*s != '\0') {
        if(*s != '\t' && *s != '\n') {
            *p2++ = *s++;
        } else {
            ++s;
        }
    }
    *p2 = '\0';
}

int main() {
    char buf[] = "this\t is\n a\t test\n test";
    strip(buf);
    printf("%s\n", buf);
}

And to appease Chris, here is a version which will make a place the result in a newly malloced buffer and return it (thus it'll work on literals). You will need to free the result.

char *strip_copy(const char *s) {
    char *p = malloc(strlen(s) + 1);
    if(p) {
        char *p2 = p;
        while(*s != '\0') {
            if(*s != '\t' && *s != '\n') {
                *p2++ = *s++;
            } else {
                ++s;
            }
        }
        *p2 = '\0';
    }
    return p;
}

Answer 2

If you want to replace \n or \t with something else, you can use the function strstr(). It returns a pointer to the first place in a function that has a certain string. For example:

// Find the first "\n".
char new_char = 't';
char* pFirstN = strstr(szMyString, "\n");
*pFirstN = new_char;

You can run that in a loop to find all \n's and \t's.

If you want to "strip" them, i.e. remove them from the string, you'll need to actually use the same method as above, but copy the contents of the string "back" every time you find a \n or \t, so that "this i\ns a test" becomes: "this is a test".

You can do that with memmove (not memcpy, since the src and dst are pointing to overlapping memory), like so:

char* temp = strstr(str, "\t");
// Remove \n.
while ((temp = strstr(str, "\n")) != NULL) {
// Len is the length of the string, from the ampersand \n, including the \n.
     int len = strlen(str);
 memmove(temp, temp + 1, len); 
}

You'll need to repeat this loop again to remove the \t's.

Note: Both of these methods work in-place. This might not be safe! (read Evan Teran's comments for details.. Also, these methods are not very efficient, although they do utilize a library function for some of the code instead of rolling your own.