C中的system()时出现分段错误

char a[200];
strcpy(a,"Hello");
printf("%s",a);

Hello

char a[200];
strcpy(a,system("echo Hello | base64"));
printf("%s",a);

aGVsbG8K
Segmentation fault

aGVsbG8K
Segmentation fault

system("echo Hello | base64")

这里 @H_502_8@

@H_502_8@

strcpy(a,system("echo Hello | base64"));

@H_502_8@system()不会将其结果存储到数组a中,因为System()作业是执行参数&中提供的命令.将它打印在控制台上,即stdout缓冲区.从system的手册页

@H_502_8@

@H_502_8@有一种方法可以解决这个问题,即不是在stdout上打印system()输出,而是可以将其输出重定向到文件&然后从文件&中读取打印.例如

@H_502_8@

int main(void) {
        close(1); /* stdout file descriptor is avilable Now */
        /* create the file if Doesn't exist,if exist truncate the content to 0 length */
        int fd = open("data.txt",O_CREAT|O_TRUNC|O_RDWR,0664); /* fd gets assigned with loWest 
                                                  available fd i.e 1 i.e NowonWARDs stdout output 
                                                  gets rediredcted to file */
        if(fd == -1) {
                /* @TODO error handling */
                return 0;
        }
        system("echo Hello | base64"); /* system output gets stored in file */
        int max_char = lseek(fd,2);/* make fd to point to end,get the max no of char */
        char *a = malloc(max_char + 1); /* to avoid buffer overflow or 
                underflow,allocate memory only equal to the max no of char in file */
        if(a == NULL) {
                /* @TODO error handling if malloc fails */
                return 0;
        }
        lseek(fd,0);/* from beginning of file */
        int ret = read(fd,a,max_char);/* Now read out put of system() from
                                          file as array and print it */
        if(ret == -1) {
                /* @TODO error handling */
                return 0;
        }
        a[ret] = '\0';/* \0 terminated array */
        dup2(0,fd);/*fd 0 duplicated to file descriptor where fd points i.e */
        printf("output : %s \n",a);
        /* to avoid memory leak,free the dynamic memory */
        free(a);
        return 0;
}

@H_502_8@我的上述建议是一个临时修复&我不会推荐这个,而是按照@chris Turner(http://man7.org/linux/man-pages/man3/popen.3.html)的建议使用[popen]

@H_502_8@

@H_502_8@例如

@H_502_8@

int main(void) {
        char buf[1024];
        FILE *fp = popen("echo Hello | base64","r");
        printf("%s\n",fgets(buf,sizeof(buf),fp));
        return 0;
}