Process and environment control

Use the process-control routines to start, stop, and manage processes from within a program. Use the environment-control routines to get and change information about the operating-system environment.

Process and environment control functions

Routine	Use
abort	Abort process without flushing buffers or calling functions registered by atexit and _onexit
assert	Test for logic error
_ASSERT, _ASSERTE macros	Similar to assert, but only available in the debug versions of the run-time libraries
atexit	Schedule routines for execution at program termination
_beginthread, _beginthreadex	Create a new thread on a Windows operating system process
_cexit	Perform exit termination procedures (such as flushing buffers), then return control to calling program without terminating process
_c_exit	Perform _exit termination procedures, then return control to calling program without terminating process
_cwait	Wait until another process terminates
_endthread, _endthreadex	Terminate a Windows operating system thread
_execl, _wexecl	Execute new process with argument list
_execle, _wexecle	Execute new process with argument list and given environment
_execlp, _wexeclp	Execute new process using PATH variable and argument list
_execlpe, _wexeclpe	Execute new process using PATH variable, given environment, and argument list
_execv, _wexecv	Execute new process with argument array
_execve, _wexecve	Execute new process with argument array and given environment
_execvp, _wexecvp	Execute new process using PATH variable and argument array
_execvpe, _wexecvpe	Execute new process using PATH variable, given environment, and argument array
exit	Call functions registered by atexit and _onexit, flush all buffers, close all open files, and terminate process
_exit	Terminate process immediately without calling atexit or _onexit or flushing buffers
getenv, _wgetenv, getenv_s, _wgetenv_s	Get value of environment variable
_getpid	Get process ID number
longjmp	Restore saved stack environment; use it to execute a nonlocal goto
_onexit	Schedule routines for execution at program termination; use for compatibility with Microsoft C/C++ version 7.0 and earlier
_pclose	Wait for new command processor and close stream on associated pipe
perror, _wperror	Print error message
_pipe	Create pipe for reading and writing
_popen, _wpopen	Create pipe and execute command
_putenv, _wputenv, _putenv_s, _wputenv_s	Add or change value of environment variable
raise	Send signal to calling process
setjmp	Save stack environment; use to execute non local goto
signal	Handle interrupt signal
_spawnl, _wspawnl	Create and execute new process with specified argument list
_spawnle, _wspawnle	Create and execute new process with specified argument list and environment
_spawnlp, _wspawnlp	Create and execute new process using PATH variable and specified argument list
_spawnlpe, _wspawnlpe	Create and execute new process using PATH variable, specified environment, and argument list
_spawnv, _wspawnv	Create and execute new process with specified argument array
_spawnve, _wspawnve	Create and execute new process with specified environment and argument array
_spawnvp, _wspawnvp	Create and execute new process using PATH variable and specified argument array
_spawnvpe, _wspawnvpe	Create and execute new process using PATH variable, specified environment, and argument array
system, _wsystem	Execute operating-system command

In the Windows operating system, the spawned process is equivalent to the spawning process. Any process can use _cwait to wait for any other process for which the process ID is known.

The difference between the _exec and _spawn families is that a _spawn function can return control from the new process to the calling process. In a _spawn function, both the calling process and the new process are present in memory unless _P_OVERLAY is specified. In an _exec function, the new process overlays the calling process, so control can't return to the calling process unless an error occurs in the attempt to start execution of the new process.

The differences among the functions in the _exec and _spawn families involve the method of locating the file to be executed as the new process, the form in which arguments are passed to the new process, and the method of setting the environment, as shown in the following table. Use a function that passes an argument list when the number of arguments is constant or is known at compile time. Use a function that passes a pointer to an array containing the arguments when the number of arguments is to be determined at run time. The information in the following table also applies to the wide-character counterparts of the _spawn and _exec functions.

_spawn and _exec Function Families

Functions	Use PATH variable to locate file	Argument-passing convention	Environment settings
_execl, _spawnl	No	List	Inherited from calling process
_execle, _spawnle	No	List	Pointer to environment table for new process passed as last argument
_execlp, _spawnlp	Yes	List	Inherited from calling process
_execvpe, _spawnvpe	Yes	Array	Pointer to environment table for new process passed as last argument
_execlpe, _spawnlpe	Yes	List	Pointer to environment table for new process passed as last argument
_execv, _spawnv	No	Array	Inherited from calling process
_execve, _spawnve	No	Array	Pointer to environment table for new process passed as last argument
_execvp, _spawnvp	Yes	Array	Inherited from calling process

See also

Universal C runtime routines by category