getenv, _wgetenv
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Header File
stdlib.h
Category
Process Control Routines
Prototype
char *getenv(const char *name);
wchar_t *_wgetenv(const wchar_t *name);
Description
Gets an environment variable from the system environment.
The environment consists of a series of entries that are of the form name=string\0.
getenv returns the value of a specified variable. name can be either uppercase or lowercase. name must not include the equal sign (=). If the specified environment variable does not exist, getenv returns a NULL pointer.
To modify an environment variable, use putenv, _wputenv.
Note: The getenv function returns a pointer to the environment variable, not a copy of the variable content. Thus it is possible to modify the content of the variable using the obtained pointer, like in the following example:
This is not the recommended way to change the content of an environment variable.char *p; p = getenv("PROCESSOR_ARCHITECTURE"); puts(p); strcpy(p, "F20"); p = getenv("PROCESSOR_ARCHITECTURE"); // has no effect on p puts(p);Possible output:
x86 F20
Return Value
On success, getenv returns the value associated with the name.
If the specified name is not defined in the environment, getenv returns a NULL pointer.
Example
#include <stdio.h>
#include <stdlib.h>
#include <alloc.h>
#include <string.h>
int main(void)
{
char *path, *ptr;
int i = 0;
/* get the current path environment */
ptr = getenv("PATH");
/* set up new path */
path = (char *) malloc(strlen(ptr)+15);
strcpy(path,"PATH=");
strcat(path,ptr);
strcat(path,";c:\\temp");
/* replace the current path and display current environment */
putenv(path);
while (_environ[i]){
printf("%s\n",_environ[i++]);
}
return 0;
}
Portability
| POSIX | Win32 | ANSI C | ANSI C++ | |
|---|---|---|---|---|
|
getenv |
+ |
+ |
+ |
+ |
|
_wgetenv |
+ |