Watcom C Library Reference : exec Functions (execl, execle,execlp, execlpe, execv, etc...)
Watcom C Reference/D - E - F 2021. 6. 23. 22:14
Watcom C Library Reference : exec Functions (execl, execle,execlp, execlpe, execv, etc...)
exec Functions
Synopsis : #include <process.h>
int execl( path, arg0, arg1 ..., argn, NULL );
int execle( path, arg0, arg1 ..., argn, NULL, envp);
int execlp( file, arg0, arg1 ..., argn, NULL);
int execlpe( file, arg0, arg1..., argn, NULL, envp);
int execv( path, argv );
int execve( path, argv, envp );
int execvp( file, argv );
int execvpe( file, argv, envp );
const char *path; /* file name incl. path */
const char *file; /* file name */
const char *arg0, ..., *argn; /* arguments */
char *const argv[ ]; /* array of arguments */
char *const envp[ ]; /* environment strings */
Description : The exec functions load and execute a new child process, named by path or file. If the child process is successfully loaded, it replaces the current process in memory. No return is made to the original program.
The program is located by using the following logic in sequence:
| 1. An attempt is made to locate the program in the current working directory if no directory specification precedes the program name; otherwise, an attempt is made in the specified directory. |
| 2. If no file extension is given, an attempt is made to find the program name, in the directory indicated in the first point, with .COM concatenated to the end of the program name. |
| 3. If no file extension is given, an attempt is made to find the program name, in the directory indicated in the first point, with .EXE concatenated to the end of the program name. |
| 4. When no directory specification is given as part of the program name, the execlp, execlpe, execvp, and execvpe functions will repeat the preceding three steps for each of the directories specified by the PATH environment variable. The command path c:\myapps; d:\lib\applns indicates that the two directories c:\myapps d: \lib\applns are to be searched. The DOS PATH command (without any directory specification) will cause the current path definition to be displayed. |
An error is detected when the program cannot be found.
Arguments are passed to the child process by supplying one or more pointers to character strings as arguments in the exec call. These character strings are concatenated with spaces inserted to separate the arguments to form one argument string for the child process. The length of this concatenated string must not exceed 128 bytes for DOS systems.
The arguments may be passed as a list of arguments (execl, execle, execlp, and execlpe) or as a vector of pointers (execv, execve, execvp, and execvpe). At least one argument, arg0 or argv[0], must be passed to the child process. By convention, this first argument is a pointer to the name of the program.
If the arguments are passed as a list, there must be a NULL pointer to mark the end of the argument list. Similarly, if a pointer to an argument vector is passed, the argument vector must be terminated by a NULL pointer.
The environment for the invoked program is inherited from the parent process when you use the execl, execlp, execv, and execvp functions. The execle, execlpe, execve, and execvpe functions allow a different environment to be passed to the child process through the envp argument. The argument envp is a pointer to an array of character pointers, each of which points to a string defining an environment variable. The array is terminated with a NULL pointer. Each pointer locates a character string of the form
variable=value
that is used to define an environment variable. If the value of envp is NULL, then the child process inherits the environment of the parent process.
The environment is the collection of environment variables whose values have been defined with the DOS SET command or by the successful execution of the putenv function. A program may read these values with the getenv function.
The execvpe and execlpe functions are extensions to POSIX 1003.1.
Returns : When the invoked program is successfully initiated, no return occurs. When an error is detected while invoking the indicated program, exec returns -1 and errno is set to the error.
Errors : When an error has occurred, errno contains a value indicating the type of error been detected.
| Constant | Meaning |
| E2BIG | The argument list exceeds 128 bytes, or the space required for the environment information exceeds 32K. |
| EACCES | The specified file has a locking or sharing violation. |
| EMFILE | Too many files open |
| ENOENT | Path or file not found |
| ENOMEM | Not enough memory is available to execute the child process. |
See Also : abort, atexit, exit, _exit, getcmd, getenv, main, putenv, spawn Functions, system
Example :
#include <stddef.h>
#include <process.h>
execl( "myprog", "myprog", "ARG1", "ARG2", NULL);
The preceding invokes "myprog" as if
myprog ARG1 ARG2
had been entered as a command to DOS. The program will be found if one of
myprog.
myprog.com
myprog.exe
is found in the current working directory.
#include <stddef.h>
#include <process.h>
char *env_list[ ] = { "SOURCE=MYDATA", "TARGET=OUTPUT", "lines=65", NULL };
execle ( "myprog", "myprog", "ARG1", "ARG2", NULL, env_list );
The preceding invokes "myprog" as if
myprog ARG1 ARG2
had been entered as a command to DOS. The program will be found if one of
myprog.
myprog.com
myprog.exe
is found in the current working directory. The DOS environment for the invoked program will consist of the three environment variables SOURCE, TARGET and lines.
#include <stddef.h>
#include <process.h>
char *arg_list[ ] = { "myprog", "ARG1", "ARG2", NULL };
execv( "myprog", arg_list );
The preceding invokes "myprog" as if
myprog ARG1 ARG2
had been entered as a command to DOS. The program will be found if one of
myprog.
myprog.com
myprog.exe
is found in the current working directory.
Classification : POSIX 1003.1 with extensions
Systems : execl - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
execle - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
execlp - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
execlpe - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
execv - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x. NT
execve - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
execvp - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
execvpe - DOS/16, QNX, OS/2 1.x(all), OS/2 2.x, NT
This manual describes the WATCOM C library for DOS, Windows, and OS/2, It includes the Standard C Library (as defined in the ANSI C Standard).
WATCOM C Language Reference manual describes the ANSI C Programming language and extensions to it which are supported by WATCOM C/C++ (32bit)
