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# std::getenv

From cppreference.com
< cpp‎ | utility‎ | program

Defined in header `<cstdlib>` |  |
const 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` (e.g. after casting away constness) invokes undefined behavior.

### [edit] Parameters

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

### [edit] Return value

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

### [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.

### [edit] Example

Run this code

    #include <iostream>
    #include <cstdlib>

    int main(int argc, char *argv[])
    {
        std::cout << "Your PATH is: " << std::getenv("PATH") << std::endl;
    }

Possible output:

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

### [edit] See also

C documentation for getenv

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