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spawnl, spawnle, spawnlp, spawnlpe, spawnv, spawnve, spawnvp, spawnvpe, _wspawnl, _wspawnle, _wspawnlp, _wspawnlpe, _wspawnv, _wspawnve, _wspawnvp, _wspawnvpe

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Header File

process.h

Category

Process Control Routines

Prototype

int spawnl(int mode, char *path, char *arg0, arg1, ..., argn, NULL);
int _wspawnl(int mode, wchar_t *path, wchar_t *arg0, arg1, ..., argn, NULL);
int spawnle(int mode, char *path, char *arg0, arg1, ..., argn, NULL, char *envp[]);
int _wspawnle(int mode, wchar_t *path, wchar_t *arg0, arg1, ..., argn, NULL, wchar_t *envp[]);
int spawnlp(int mode, char *path, char *arg0, arg1, ..., argn, NULL);
int _wspawnlp(int mode, wchar_t *path, wchar_t *arg0, arg1, ..., argn, NULL);
int spawnlpe(int mode, char *path, char *arg0, arg1, ..., argn, NULL, char *envp[]);
int _wspawnlpe(int mode, wchar_t *path, wchar_t *arg0, arg1, ..., argn, NULL, wchar_t *envp[]);
int spawnv(int mode, char *path, char *argv[]);
int _wspawnv(int mode, wchar_t *path, wchar_t *argv[]);
int spawnve(int mode, char *path, char *argv[], char *envp[]);
int _wspawnve(int mode, wchar_t *path, wchar_t *argv[], wchar_t *envp[]);
int spawnvp(int mode, char *path, char *argv[]);
int _wspawnvp(int mode, wchar_t *path, wchar_t *argv[]);
int spawnvpe(int mode, char *path, char *argv[], char *envp[]);
int _wspawnvpe(int mode, wchar_t *path, wchar_t *argv[], wchar_t *envp[]);
Note: In spawnle, spawnlpe, spawnv, spawnve, spawnvp, and spawnvpe, the last string must be NULL.

Description

The functions in the spawn... family create and run (execute) other files, known as child processes. There must be sufficient memory available for loading and executing a child process.

The value of mode determines what action the calling function (the parent process) takes after the spawn... call. The possible values of mode are

P_WAIT

Puts parent process on hold until child process completes execution.

P_NOWAIT

Continues to run parent process while child process runs. The child process ID is returned, so that the parent can wait for completion using cwait or wait.

P_NOWAITO

Identical to P_NOWAIT except that the child process ID isn't saved by the operating system, so the parent process can't wait for it using cwait or wait.

P_DETACH

Identical to P_NOWAITO, except that the child process is executed in the background with no access to the keyboard or the display.

P_OVERLAY

Overlays child process in memory location formerly occupied by parent. Same as an exec... call.



path is the file name of the called child process. The spawn... function calls search for path using the standard operating system search algorithm:

  • If there is no extension or no period, they search for an exact file name. If the file is not found, they search for files first with the extension EXE, then COM, and finally BAT.
  • If an extension is given, they search only for the exact file name.
  • If only a period is given, they search only for the file name with no extension.
  • If path does not contain an explicit directory, spawn... functions that have the p suffix search the current directory, then the directories set with the operating system PATH environment variable.

The suffixes p, l, and v, and e added to the spawn... "family name" specify that the named function operates with certain capabilities.

p

The function searches for the file in those directories specified by the PATH environment variable. Without the p suffix, the function searches only the current working directory.

l

The argument pointers arg0, arg1, ..., argn are passed as separate arguments. Typically, the l suffix is used when you know in advance the number of arguments to be passed.

v

The argument pointers argv[0], ..., arg[n] are passed as an array of pointers. Typically, the v suffix is used when a variable number of arguments is to be passed.

e

The argument envp can be passed to the child process, letting you alter the environment for the child process. Without the e suffix, child processes inherit the environment of the parent process.



Each function in the spawn... family must have one of the two argument-specifying suffixes (either l or v). The path search and environment inheritance suffixes (p and e) are optional.

For example:

  • spawnl takes separate arguments, searches only the current directory for the child, and passes on the parent's environment to the child.
  • spawnvpe takes an array of argument pointers, incorporates PATH in its search for the child process, and accepts the envp argument for altering the child's environment.

The spawn... functions must pass at least one argument to the child process (arg0 or argv[0]). This argument is, by convention, a copy of path. (Using a different value for this 0 argument won't produce an error.) If you want to pass an empty argument list to the child process, then arg0 or argv[0] must be NULL.

When the l suffix is used, arg0 usually points to path, and arg1, ...., argn point to character strings that form the new list of arguments. A mandatory null following argn marks the end of the list.

When the e suffix is used, you pass a list of new environment settings through the argument envp. This environment argument is an array of character pointers. Each element points to a null-terminated character string of the form

envvar = value

where envvar is the name of an environment variable, and value is the string value to which envvar is set. The last element in envp[] is null. When envp is null, the child inherits the parents' environment settings.

The combined length of arg0 + arg1 + ... + argn (or of argv[0] + argv[1] + ... + argv[n]), including space characters that separate the arguments, must be less than 260 bytes for Windows (128 for DOS). Null-terminators are not counted.

When a spawn... function call is made, any open files remain open in the child process.

Return Value

When successful, the spawn... functions, where mode is P_WAIT, return the child process' exit status (0 for a normal termination). If the child specifically calls exit with a nonzero argument, its exit status can be set to a nonzero value.

If mode is P_NOWAIT or P_NOWAITO, the spawn functions return the process ID of the child process. The ID obtained when using P_NOWAIT can be passed to cwait.

On error, the spawn... functions return -1, and the global variable errno is set to one of the following values:

E2BIG

Arg list too long

EINVAL

Invalid argument

ENOENT

Path or file name not found

ENOEXEC

Exec format error

ENOMEM

Not enough memory



Example

#include <process.h>
#include <stdio.h>
void spawnl_example(void)
{
   int result;
   result = spawnl(P_WAIT, "bcc32.exe", "bcc32.exe", NULL);
   if (result == -1)
   {
      perror("Error from spawnl");
      exit(1);
   }
}
int main(void)
{
  spawnl_example();
  return 0;
}
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