std::getenv
Defined in header
<cstdlib>
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char* getenv( const char* env_var );
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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.
Contents |
[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
#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
[edit] See also
C documentation for getenv
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