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C Tutorial - Strings and Text Handling

By David Bolton, About.com Guide

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Using the str Functions

There are quite a number of these but you'll probably only need these that are listed below

strcat() - concatenate two strings.
strcpy() - copy a string (handy for doing string assignments).
strcmp() - compare two strings.
strlen() - return the length of a string- this does not include the terminating zero.
strchr() - find a character in a string searching from left.

You also get strn.. versions of the first three (not strlen( and strchr) with an extra parameter size_t n

strncat().
strncpy().
strncmp().

These limit the operation to the first n chars. For instance strncat() appends a maximum of n chars from a string to another string.

Memory Management

You are responsible for making sure that strings are properly allocated and freed. For instance this

string a="A very Long String";
string b=strcat(a," and now even longer!") ;

While it looks ok is a guaranteed disaster. The first line executes fine but the second takes exception. The strcat() function does not allocate any memory. The compiler would perceive this text as being read-only so it's probably located somewhere that cannot be written to. In this case you must allocate enough space to store the combined strings.

Example 4 demonstrates this correctly:

Download Example 4.

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

typedef char * string;

int main(int argc, char* argv[])
{

  string a="A very Long String";
  string b=" and now even longer!";
  string c=malloc(strlen(a) + strlen(b)+1) ; /* +1 DFTTZ! */
  strcpy(c,a) ;
  strcat(c,b) ;
  printf("c = %s",c) ;
  free(c) ;
  return 0;
}