String Functions

The C language provides no explicit support for strings in the language itself. The string-handling functions are implemented in libraries. String I/O operations are implemented in <stdio.h> (puts , gets, etc). A set of simple string manipulation functions are implemented in <string.h>, or on some systems in <strings.h>.

The string library (string.h or strings.h) has some useful functions for working with strings, like strcpy, strcat, strcmp, strlen, strcoll, etc. We will take a look at some of these string operations.

Important: Don’t forget to include the library string.h (or on some systems strings.h) if you want to use one of these library functions.

strcpy

This library function is used to copy a string and can be used like this: strcpy(destination, source). (It is not possible in C to do this: string1 = string2). Take a look at the following example:

 str_one = "abc";
 str_two = "def";
 strcpy(str_one , str_two); // str_one becomes "def"

Note: strcpy() will not perform any boundary checking, and thus there is a risk of overrunning the strings.

strcmp

This library function is used to compare two strings and can be used like this: strcmp(str1, str2).

• If the first string is greater than the second string a number greater than null is returned.
• If the first string is less than the second string a number less than null is returned.
• If the first and the second string are equal a null is returned.

Take look at an example:

 printf("Enter you name: ");
 scanf("%s", name);
 if( strcmp( name, "jane" ) == 0 )
  printf("Hello, jane!\n");

Note: strcmp() will not perform any boundary checking, and thus there is a risk of overrunning the strings.

strcat

This library function concatenates a string onto the end of the other string. The result is returned. Take a look at the example:

 printf("Enter you age: ");
 scanf("%s", age);
 result = strcat( age, " years old." ) == 0 )
 printf("You are %s\n", result);

Note: strcat() will not perform any boundary checking, and thus there is a risk of overrunning the strings.

strlen

This library function returns the length of a string. (All characters before the null termination.) Take a look at the example:

 name = "jane";
 result = strlen(name); //Will return size of four.

memcmp

This library function compares the first count characters of buffer1 and buffer2. The function is used like this: memcmp(buffer1,buffer2). The return values are as follows:

• If buffer1 is greater than buffer2 a number greater than null is returned.
• If buffer1 is less than buffer2 a number less than null is returned.
• If buffer1 and buffer2 are equal a null is returned.

Note: There are also library functions: memcpy, memset and memchr.

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