exec配合fork使用

exec配合fork使用

实现功能，当父进程检测到输入为1的时候，创建子进程把配置文件的字段值修改掉。

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

int main()
{
        pid_t pid;
        int data = 0;
        while(1){
                printf("please input a data\n");
                scanf("%d", &data);
                if(data == 1){
                        pid = fork();
                        if(pid > 0){
                                wait(NULL);
                        }

                        if(pid == 0){
                                int fdSrc;
                                char *readBuf = NULL;

                                fdSrc = open("config.txt", O_RDWR);

                                int size = lseek(fdSrc, 0, SEEK_END);
                                lseek(fdSrc, 0, SEEK_SET);

                                readBuf = (char *)malloc(sizeof(char) * size + 8);
                                int n_read = read(fdSrc, readBuf, size);

                                char *p = strstr(readBuf, "LENG=");
                                if(p == NULL){
                                        printf("not found \n");
										exit(-1);
                                }
                                p = p + strlen("LENG=");
                                *p = '8';
                                lseek(fdSrc, 0, SEEK_SET);
                                int n_write = write(fdSrc, readBuf, strlen(readBuf));

                                close(fdSrc);
                                exit(0);
                        }
                }else{
                        printf("wait, do nothing\n");
                }
        }
        return 0;
}

这样看，子进程里面的代码会变得特别复杂

下面使用 execl 来进行简化

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

int main()
{
        pid_t pid;
        int data = 0;
        while(1){
                printf("please input a data\n");
                scanf("%d", &data);
                if(data == 1){
                        pid = fork();
                        if(pid > 0){
                                wait(NULL);
                        }

                        if(pid == 0){
                                execl("./changeData", "changeData", "config.txt", NULL);
                                exit(0);
                        }
                }else{
                        printf("wait, do nothing\n");
                }
        }
        return 0;
}