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getenv, getenv_s

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)
-1) 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.
-2) 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 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>.
-
-

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)

Return value

-1) character string identifying the value of the environmental variable or null pointer if such variable is not found.
-2) 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).

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.

-

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

References

See also

-
C++ documentation for getenv
-

- © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
- https://en.cppreference.com/w/c/program/getenv -

-
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