0901假設(shè)存在一個可以從標準輸入讀入字母并且將其從小寫轉(zhuǎn)換為大寫輸出的可執(zhí)行程序upcase

/*

• 假設(shè)存在一個可以從標準輸入讀入字母并且將其從小寫轉(zhuǎn)換為大寫輸出的可執(zhí)行程序upcase,
• 使用pipe函數(shù)編寫一個應(yīng)用程序，實現(xiàn)將一個指定文本文件中的字母都轉(zhuǎn)換為大寫。
  */

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

#define BUFSIZE PIPE_BUF

int main(int argc, char argv[])
{
int n,fd[2];
pid_t pid;
char buffer[BUFSIZE+1];
FILE fp;
if(argc<=1)
{
printf("usage:%s <pathname>\n",argv[0]);
exit(1);
}
//open txt file
if((fp=fopen(argv[1],"r"))==NULL)
{
printf("Can't open %s\n",argv[1]);
exit(1);
}
//create pipe
if(pipe(fd)<0)
{
printf("pipe failed!\n");
exit(1);
}
//create son process
if((pid=fork())<0)
{
printf("fork failed!\n");
exit(1);
}
else if(pid>0)// father process
{
close(fd[0]);
while(fgets(buffer,BUFSIZE,fp)!=NULL)
{
n=strlen(buffer);
//write data to pipe
if(write(fd[1],buffer,n)!=n)
{
printf("write error to pipe.\n");
exit(1);
}
}
if(ferror(fp))
{
printf("fgets error.\n");
exit(1);
}
close(fd[1]);
if(waitpid(pid,NULL,0)<0)
{
printf("waitpid error!\n");
exit(1);
}
exit(0);
}
else
{
close(fd[1]);
if(fd[0]!=STDIN_FILENO)
{
//copy pipe to stdin
if(dup2(fd[0],STDIN_FILENO)!=STDIN_FILENO)
{
printf("dup2 error to stdin!\n");
exit(1);
}
close(fd[0]);
}
//run user program
if(execl("upcase","upcase",(char *)0)<0)
{
printf("execl error for upcase.\n");
exit(1);
}
exit(0);
}
//return 0;
}