strstr:

Syntax:

#include <string.h>
char *strstr( const char *str1, const char *str2 );

The function strstr() returns a pointer to the first occurrence of str2 in str1, or NULL if no match is found. If the length of str2 is zero, then strstr() will simply return str1.

For example, the following code checks for the existence of one string within another string:

 char* str1 = "this is a string of characters";
 char* str2 = "a string";
 char* result = strstr( str1, str2 );
 if( result == NULL ) printf( "Could not find '%s' in '%s'\n", str2, str1 );
 else printf( "Found a substring: '%s'\n", result );

When run, the above code displays this output:

 Found a substring: 'a string of chara

memchr: Syntax: #include <string.h>
void *memchr( const void *buffer, int ch, size_t count );

The memchr() function looks for the first occurrence of ch within count characters in the array pointed to by buffer. The return value points to the location of the first occurrence of ch, or NULL if ch isn't found. For example:

char names[] = "Alan Bob Chris X Dave";
if( memchr(names,'X',strlen(names)) == NULL )
    printf( "Didn't find an X\n" );
else
    printf( "Found an X\n" );

memcmp:
Syntax:

 #include <string.h>
 int memcmp( const void *buffer1, const void *buffer2, size_t count );

The function memcmp() compares the first count characters of buffer1 and buffer2. The return values are as follows:

Value	Explanation
less than 0	buffer1 is less than buffer2
equal to 0	buffer1 is equal to buffer2
greater than 0	buffer1 is greater than buffer2

 Standard C String:

atof	converts a string to a double
atoi	converts a string to an integer
atol	converts a string to a long
isalnum	true if a character is alphanumeric
isalpha	true if a character is alphabetic
iscntrl	true if a character is a control character
isdigit	true if a character is a digit
isgraph	true if a character is a graphical character
islower	true if a character is lowercase
isprint	true if a character is a printing character
ispunct	true if a character is punctuation
isspace	true if a character is a space character
isupper	true if a character is an uppercase character
isxdigit	true if a character is a hexidecimal character
memchr	searches an array for the first occurance of a character
memcmp	compares two buffers
memcpy	copies one buffer to another
memmove	moves one buffer to another
memset	fills a buffer with a character
strcat	concatenates two strings
strchr	finds the first occurance of a character in a string
strcmp	compares two strings
strcoll	compares two strings in accordance to the current locale
strcpy	copies one string to another
strcspn	searches one string for any characters in another
strerror	returns a text version of a given error code
strlen	returns the length of a given string
strncat	concatenates a certain amount of characters of two strings
strncmp	compares a certain amount of characters of two strings
strncpy	copies a certain amount of characters from one string to another
strpbrk	finds the first location of any character in one string, in another string
strrchr	finds the last occurance of a character in a string
strspn	returns the length of a substring of characters of a string
strstr	finds the first occurance of a substring of characters
strtod	converts a string to a double
strtok	finds the next token in a string
strtol	converts a string to a long
strtoul	converts a string to an unsigned long
strxfrm	converts a substring so that it can be used by string comparison functions
tolower	converts a character to lowercase
toupper	converts a character to uppercase

C/C++ Reference:

http://www.cppreference.com/index.html