CHAPTER 47. STRINGS TRIMMING CHAPTER 47. STRINGS TRIMMING

Chapter 47

Strings trimming

A very common string processing task is to remove some characters at the start and/or at the end.

In this example, we are going to work with a function which removes all newline characters (CR^1 /LF^2 ) from the end of the
input string:

#include <stdio.h>
#include <string.h>

char str_trim (char s)
{
char c;
size_t str_len;

// work as long as \r or \n is at the end of string
// stop if some other character there or its an empty string'
// (at start or due to our operation)
for (str_len=strlen(s); str_len>0 && (c=s[str_len-1]); str_len--)
{
if (c=='\r' || c=='\n')
s[str_len-1]=0;
else
break;
};
return s;
};

int main()
{
// test

// strdup() is used to copy text string into data segment,

// because it will crash on Linux otherwise,

// where text strings are allocated in constant data segment,

// and not modifiable.

printf ("[%s]\n", str_trim (strdup("")));
printf ("[%s]\n", str_trim (strdup("\n")));
printf ("[%s]\n", str_trim (strdup("\r")));
printf ("[%s]\n", str_trim (strdup("\n\r")));
printf ("[%s]\n", str_trim (strdup("\r\n")));
printf ("[%s]\n", str_trim (strdup("test1\r\n")));
printf ("[%s]\n", str_trim (strdup("test2\n\r")));
printf ("[%s]\n", str_trim (strdup("test3\n\r\n\r")));
printf ("[%s]\n", str_trim (strdup("test4\n")));
printf ("[%s]\n", str_trim (strdup("test5\r")));
printf ("[%s]\n", str_trim (strdup("test6\r\r\r")));
};

The input argument is always returned on exit, this is convenient when you need to chain string processing functions, like it
was done here in themain()function.

(^1) Carriage return (13 or’\r’ in C/C++)
(^2) Line feed (10 or’\n’ in C/C++)