Linux C library function Encyclopedia: Environmental variable Control function

1.GETENV (Get environment variable content)

Related functions:

Putenv,setenv,unsetenv

Table header file:

#include <stdlib.h>

To define a function:

char * getenv (const char *name);

Function Description:

Getenv () is used to get the contents of the parameter name environment variable. The parameter name is the name of the environment variable, and a pointer to that content is returned if the variable exists. The format of the environment variable is name=value.

return value:

Successful execution returns a pointer to the content, and null if no match is found for the environment variable name.

Example:

#include <stdio.h> 
#include <sys/types.h> 
#include <sys/stat.h> 
#include <fcntl.h > 
#include <stdlib.h> 
main () 
{ 
    char *p; 
    if (p = getenv ("USER")) 
        printf ("user=%s\n", p); 

2.putenv (change or increase environment variable)

Related functions:

Getenv,setenv,unsetenv

Table header file:

#include4 <stdlib.h>

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