You can access the builtin C library functions through header files. The string related functions are located in String.h file.
Each function listed below has a specific purpose.
| Function | Description |
|---|---|
| strlen() | To find the length of a string. |
| strlwr() | Converts a string to lowercase. |
| strupr() | Converts a string to uppercase. |
| strcat() | Add one string to another to make a bigger string. |
| strncat() | Add n character of a string to another string |
| strcpy() | Copies a string to another string replaces any existing. |
| strcmp() | Compare two strings. |
| strncpy() | Copies first n characters of two strings. |
| strncmp() | Compares only first n characters with another string. |
| stricmp() | Compare two strings, disregards case. |
| strcmpi() | Same as stricmp() |
| strncmp() | Compares first n characters of two strings. |
| strnicmp() | Compares first n characters of two strings, disregards case |
| strdup() | Duplicate a string. |
| strchr() | Finds first occurrence of a given character in a string. |
| strrchr() | Finds last occurrence of a given character in a string. |
| strstr() | Finds first occurrence of a given string in another string. |
| strset() | Changes all characters of a string to given character. |
| strnset() | Changes first n char of a string to given character. |
| strrev() | Reverse a given string. |
From the above table, 
, 
, 
and 
are the most frequently used functions.
C Library String Functions Example
You will write a program that implement these 
built-in functions.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char str[] = "Chile";
char str2[] = "India";
int len1;
int len2;
int boo;
/* Implement strlen() function */
len1 = strlen(str);
len2 = strlen(str2);
printf("Length of First String = %d\n",len1);
printf("Length of Second String = %d\n",len2);
boo = strcmp(str2,str);
if(boo > 0)
{
printf("String Mismatch\n");
}
else
{
printf("String Matched\n");
}
strcat(str,str2);
printf("string cat = %s\n",str);
strcpy(str,str2);
printf("string copy = %s\n",str);
system("PAUSE");
return 0;
}Output
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Length of First String = 5
Length of Second String = 5
String Mismatch
string cat = ChileIndia
string copy = India
Press any key to continue . . . 