Standard Pipe (popen), standard pipe popen

Standard Pipe (popen), standard pipe popen

NAME       popen, pclose - pipe stream to or from a processSYNOPSIS       #include <stdio.h>       FILE *popen(const char *command, const char *type);       int pclose(FILE *stream);DESCRIPTION       The popen() function opens a process by creating a pipe,  forking,  and       invoking  the shell.  Since a pipe is by definition unidirectional, the       type argument may specify  only  reading  or  writing,  not  both;  the       resulting stream is correspondingly read-only or write-only.       The  command argument is a pointer to a null-terminated string contain-       ing a shell command line.  This command is passed to /bin/sh using  the       -c  flag;  interpretation, if any, is performed by the shell. RETURN VALUE       The popen() function returns NULL if the fork(2) or pipe(2) calls fail,       or if it cannot allocate memory.       The pclose() function returns -1 if wait4(2) returns an error, or  some       other error is detected.

Write

Popen. c, as follows:

/*************************************************************************    > File Name: popen.c    > Author: KrisChou    > Mail:zhoujx0219@163.com     > Created Time: Fri 22 Aug 2014 11:07:26 AM CST ************************************************************************/#include <stdio.h>#include <stdlib.h>#include <string.h>int main(int argc, char *argv[]){    char buf[1024];    FILE *fp;        while(memset(buf,0,1024),fgets(buf,1024,stdin) != NULL)    {        fp = popen(argv[1],"w");        fputs(buf,fp);        pclose(fp);    }    return 0;}

The called function reverse. c is as follows:

/*************************************** * *********************************> File Name: reverse. c> Author: KrisChou> Mail: zhoujx0219@163.com> Created Time: sat 23 Aug 2014 11:21:27 am cst ********************************* ***************************************/ # include <stdio. h> # include <stdlib. h> # include <string. h> int main (int argc, char * argv []) {char word [256]; // read the string char buf [256] [256] from the standard input , Index = 0; // Save the string while (memset (word, 0,256), scanf ("% s", word) read from the standard input )! = EOF) {strcpy (buf [index ++], word) ;}index --; while (index> = 0) {printf ("% s ", buf [index]); index --;} printf ("\ n"); return 0 ;}

Run the program:

[purple@localhost popen]$ gcc popen.c -o main[purple@localhost popen]$ gcc reverse.c -o reverse[purple@localhost popen]$ ./main ./reversehow are youyou are howbaby u r beautifulbeautiful r u baby[purple@localhost popen]$

Press ctrl + D to exit the loop in popen. c and exit the program.

LinuxC for popen, pclose

This function should be used to read the content in the current directory.
Popen can start a new process, and ls-l is the name and parameter of the program to be started. Of course, even if the directory is listed
"R" indicates that the calling process can read the output of the newly started process through the returned file pointer. It can also be "w", so that the calling process can read from the standard input by writing content to the file and the newly started process. In fact, this is the pipeline communication between processes.
Popen returns a file pointer. If the returned NULL pointer is 0, an error occurs.
The following while LOOP reads the content of the returned file to the file pointed to by the passed sck file descriptor. fileno converts the file pointer to the file descriptor.
The pclose function closes the pipeline. The returned value is the exit code of the newly started program,
In general, if the program returns 0, it indicates that it is correct. If the value is non-zero, it indicates that the program may be faulty. If the pclose function is incorrect, it will return-1.

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