getenv, getenv_s - cppreference.com (original) (raw)

Defined in header <stdlib.h>
char getenv( const char name );	(1)
errno_t getenv_s( size_t restrict len, char restrict value, rsize_t valuesz, const char *restrict name );	(2)	(since C11)

Searches for an environmental variable with name name in the host-specified environment list and returns a pointer to the string that is associated with the matched environment variable. The set of environmental variables and methods of altering it are implementation-defined.

This function is not required to be thread-safe. Another call to getenv, as well as a call to the POSIX functions setenv(), unsetenv(), and putenv() may invalidate the pointer returned by a previous call or modify the string obtained from a previous call.

Modifying the string returned by getenv invokes undefined behavior.

Same as (1), except that the values of the environment variable is written to the user-provided buffer value (unless null) and the number of bytes written is stored in the user-provided location *len (unless null). If the environment variable is not set in the environment, zero is written to *len (unless null) and '\0' is written to value[0] (unless null). In addition, the following errors are detected at runtime and call the currently installed constraint handler function:

name is a null pointer
valuesz is greater than RSIZE_MAX
value is a null pointer and valuesz is not zero

As with all bounds-checked functions, getenv_s is only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdlib.h>.

[edit] Parameters

name	-	null-terminated character string identifying the name of the environmental variable to look for
len	-	pointer to a user-provided location where getenv_s will store the length of the environment variable
value	-	pointer to a user-provided character array where getenv_s will store the contents of the environment variable
valuesz	-	maximum number of characters that getenv_s is allowed to write to dest (size of the buffer)

[edit] Return value

character string identifying the value of the environmental variable or null pointer if such variable is not found.
zero if the environment variable was found, non-zero if it was not found or if a runtime constraint violation occurred. On any error, writes zero to *len (unless len is a null pointer).

[edit] Notes

On POSIX systems, the environment variables are also accessible through the global variable environ, declared as extern char **environ; in <unistd.h>, and through the optional third argument, envp, of the main function.

The call to getenv_s with a null pointer for value and zero for valuesz is used to determine the size of the buffer required to hold the entire result.

[edit] Example

#include <stdio.h> #include <stdlib.h> int main(void) { const char *name = "PATH"; const char *env_p = getenv(name); if (env_p) printf("Your %s is %s\n", name, env_p); }

Possible output:

Your PATH is /home/gamer/.local/bin:/usr/local/bin:/usr/bin:/bin:/usr/share/games

[edit] References