Linux Learning-1 process

In Linux, another program is launched inside a program to create a new process.1.This work can be done through the library function system.

#include <stdlib.h>

int system (const char *string);

The function of the system function is to run the command as a string parameter and wait for the command to complete. The execution of the command is like executing the following command in the shell:

$ sh-c String

If the shell cannot be started to run this command, the system function returns error code 127, and the other error returns-1.

System.c

#include <stdlib.h>#include<stdio.h>int  main () {    printf ("  Running Upper with system\n");    System ("./upper");    printf ("done.\n");    Exit (0);}

Compiling GCC system.c-o system

At execution time./system

You will find that the upper program is executed.

2. Create the process bottom interface exec.

The EXEC series function consists of a set of related functions that differ in how the process is started and how the program parameters are expressed. The EXEC function can replace the current process with a new process. You can use the EXEC function to switch the execution of a program from one program to another.

The EXEC function is more efficient than the system function because the original program is no longer running after the new program starts.

#include <unistd.h>

int execl (XXX);

int EXECLP (XXX);

int execle (XXX);

int execv (XXX);

int EXECVP (XXX);

int execve (XXX);

Or take the upper program as an example:

Exe_up.c

 #include <stdio.h> #include  <unistd.h>  #include  <stdlib.h>int   main () {printf (  " runing    With execlp\n   " ); EXECLP (  " ./upper  " ,  " /upper   "   " down   "     0    

GCC Exe_up.c-o exe_up

./exe_up

Ps:

Upper.c

#include <stdio.h>#include<stdlib.h>#include<ctype.h>int  main () {    int  ch;      while (EOF! = (ch=getchar ())    ) {        Putchar (toupper (CH));    }    Exit (0);    }

GCC Upper.c-o Upper

All of the above is from the fourth edition of Linux programming.

Linux Learning-1 process