Linux fork 多进程 实现拷贝文件 四个进程拷贝

[kxh1234]

Linux fork 多进程 实现拷贝文件
四个进程拷贝
我的代码

请各位帮我找找问题

#include<stdio.h>
#include<sys/wait.h>
#include<string.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<stdlib.h>  
int main(int argc,char *argv[])
{

char buf[1024];
int fd=open(argv[1],O_RDONLY);
if(fd==-1)
{
perror("open source file failed!");
exit(1);
}

int fd1=open(argv[2],O_WRONLY |O_CREAT| O_EXCL,0777);
if(fd1==-1)
{
perror("open tap file failed!");
exit(1);
}

int len=lseek(fd,0,SEEK_END);

if(len==-1)
{
perror("lseek failed!");
exit(1);
}
int block_size=len%4+1;
//	char *buf=NULL;
//char buf[1024];
int i=0;
int pid;
for(i=0;i<3;i++)
{
pid=fork();
if(pid==0)
break;

}
int n=read(fd,buf,block_size);
if(n<0)
{
perror("read failed!");
exit(0);
}
int m=write(fd1,buf,n);

if(pid>0)
while(wait(NULL));

//free(buf);
close(fd);
close(fd1);
return 0；

} 

[LubinLew]

lseek 用于计算文件长度后没有使用lseek(fd, 0 SEEK_SET);复归文件指针,导致文件指针一直指向文件末尾,读文件时获取不到文件内容. 父进程不能无限等待wait, 就应该等待3个wait 这样拷贝文件可能会导致内容乱序

#include<stdio.h>
#include<sys/wait.h>
#include<string.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<stdlib.h>

int main(int argc, char *argv[])
{
	char buf[1024];
	pid_t parent;

	parent =  getpid();
	printf("=== Parent PID:%d\n", parent);
	
	int fd = open(argv[1], O_RDONLY);
	if (fd == -1) {
		perror("open source file failed!");
		exit(1);
	}

	int fd1 = open(argv[2], O_WRONLY | O_CREAT | O_EXCL, 0777);
	if (fd1 == -1) {
		perror("open tap file failed!");
		exit(1);
	}
 
	off_t len = lseek(fd, 0, SEEK_END);
	if (len == (off_t)-1) {
		perror("lseek failed!");
		exit(1);
	}
	//rewind
	lseek(fd, 0, SEEK_SET);

	int block_size = len / 4 + 1;
	printf("=== source file len=%ld, block_size=%d\n", len, block_size);
	int i = 0;
	int pid;
	for (i = 0; i < 3; i++) {
		pid = fork();
		if (pid == 0) /* child */
			break;
	}

	int n = read(fd, buf, block_size);
	if(n < 0) {
		perror("read failed!");
		exit(0);
	}
	printf("=== PID:%d, parent PID:%d, Read %d bytes [%s]\n", getpid(), getppid(),n, buf);
	
	int m = write(fd1, buf, n);

	//wait 3 child
	if (getpid() == parent) {
		for (i = 0; i < 3; i++) {
			wait(NULL);
		}
	}

	close(fd);
	close(fd1);

	return 0;
}