std::getenv

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

Variadic functions

Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

Pairs and tuples

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Type operations

declval (C++11)

as_const (C++17)

 

Program support utilities

Program termination
abort exit quick_exit (C++11) _Exit (C++11)	atexit at_quick_exit (C++11) EXIT_SUCCESSEXIT_FAILURE
Communicating with the environment
system	getenv
Signals
signal raise sig_atomic_t	SIG_DFLSIG_IGN SIG_ERR
Signal types
SIGABRTSIGFPESIGILLSIGINTSIGSEGVSIGTERM
Non-local jumps
setjmp
longjmp
Types
jmp_buf

 

Defined in header <cstdlib>
char* getenv( const char* env_var );

Searches the environment list provided by the host environment (the OS), for a string that matches the C string pointed to by env_var and returns a pointer to the C string that is associated with the matched environment list member.

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.	(until C++11)
This function is thread-safe (calling it from multiple threads does not introduce a data race) as long as no other function modifies the host environment. In particular, the POSIX functions setenv(), unsetenv(), and putenv() would introduce a data race if called without synchronization.	(since C++11)

Modifying the string returned by getenv invokes undefined behavior.

Parameters

env_var

-

null-terminated character string identifying the name of the environmental variable to look for

Return value

Character string identifying the value of the environmental variable or null pointer if such variable is not found.

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.

Example

Run this code

#include <iostream>
#include <cstdlib>
 
int main()
{
    if(const char* env_p = std::getenv("PATH"))
        std::cout << "Your PATH is: " << env_p << '\n';
}

Possible output:

Your PATH is: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

See also

C documentation for getenv