Question

我有一个程序，它将两个文件作为参数。第一个文件将被复制到第二个文件中。该程序分为2个子节点，第一个子节点读取文件并通过管道将其抛出到另一个子节点，然后另一个子节点将其写入文件。这两个文件最终应该是相同的。

当我运行diff来比较这两个文件时，我收到以下错误：

virtual@ubuntu:~/Documents/OSprojects$ ./parent test.txt test2.txt
virtual@ubuntu:~/Documents/OSprojects$ cat test.txt
123456789112233445566778899
virtual@ubuntu:~/Documents/OSprojects$ cat test2.txt
123456789112233445566778899
virtual@ubuntu:~/Documents/OSprojects$ diff test.txt test2.txt
Binary files test.txt and test2.txt differ
virtual@ubuntu:~/Documents/OSprojects$

正如你所看到的那样，它们都是相同的，但差异打印出它们是不同的。显然它只是我对diff cmd不了解的东西。任何帮助将不胜感激。

我相信由于某种原因，我创建的文件是二进制文件而第一个文件不是，但我不知道为什么它是二进制文件。我相信它可能与这行代码有关：

    write(1, buf, BUF_SIZE);            //write to buffer
    memset(buf, '\0', BUF_SIZE);

在其中一个孩子中，这是写入缓冲区然后我正在清除缓冲区。我清除那个缓冲区了吗？

以下是cat -e：

的结果

virtual@ubuntu:~/Documents/OSprojects$ cat -e test2.txt
123456789112233445566778899$
^@^@^@^@virtual@ubuntu:~/Documents/OSprojects$

以下是cmp：

的结果

virtual@ubuntu:~/Documents/OSprojects$ cmp test.txt test2.txt
cmp: EOF on test.txt
virtual@ubuntu:~/Documents/OSprojects$

我相信这是我的问题，我怎样才能清除那个缓冲区，以便它最终不会抛出那些？

我的所有代码::

父：

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

#define BUF_SIZE 16

void exitWithError(char* errorMsg, int exitWith);       //generic error out function
void launch_writer(const char* pathname, char* const argv[], int pfd[]);    
void launch_reader(const char* pathname, char* const argv[], int pfd[]);   

int main(int argc, char* argv[]){

//making the pipe
int pfd[2];
if(pipe(pfd) == -1) //test pipe creation
    exitWithError("PIPE FAILED", 1);

//forking
pid_t reader_child_pid;
pid_t writer_child_pid;

//args for each fork
char *args_1[] = {"reader", argv[1], (char *) 0};
char *args_2[] = {"writer", argv[2], (char *) 0};

if((writer_child_pid = fork()) == -1) {
    exitWithError("WRITER FORK FAILED", 1);
}
else if (writer_child_pid == 0) {       //first child comes here
    launch_writer("./writer", args_2, pfd);
}
else if ((reader_child_pid = fork()) == -1) {
    exitWithError("READER FORK FAILED", 1);
}
else if (reader_child_pid == 0) {       //second child comes here
    launch_reader("./reader", args_1, pfd);
}

//parent picks up here

//close off pipe from parents end
close(pfd[0]);
close(pfd[1]);


//wait for all processes to exit before ending
for(;;) {
    if(wait(NULL) == -1){
        if(errno == ECHILD)
            exit(0);
        else {
            exitWithError("WAIT ERROR", 1);
        }
    }
}
}

void exitWithError(char* errorMsg, int exitWith) {
perror(errorMsg);
exit(exitWith);
}

void launch_writer(const char* pathname, char* const argv[], int pfd[]) {
dup2(pfd[0], 0);
close(pfd[1]);
close(pfd[0]);
execve(pathname, argv, NULL);
perror("execve failed");
}

void launch_reader(const char* pathname, char* const argv[], int pfd[]) {
dup2(pfd[1], 1);
close(pfd[1]);
close(pfd[0]);
execve(pathname, argv, NULL);
perror("execve failed");
}

孩子1：

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

#define BUF_SIZE 16

int main(int argc, char* argv[]){
//Opens file to be read from
int inFile = open(argv[1], O_RDONLY);

//declaring variables
char buf[BUF_SIZE]; //temp hold whats read/written
int read_test;      //check if EOF
for(;;) {
    read_test = read(inFile, buf, BUF_SIZE);    //read from file
    if(read_test == 0) //eof
        break;
    write(1, buf, BUF_SIZE);            //write to buffer
    memset(buf, '\0', BUF_SIZE);
}
close(inFile);
exit(0);
}

孩子2：

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

#define BUF_SIZE 16

int main(int argc, char* argv[]){
//Opens a file for reading/writing, if exists then truncates, otherwise makes new one
//with correct permissions
int wri_inFile = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC , S_IRUSR | S_IWUSR);
if(wri_inFile == -1)
    perror("ERROR OPENING FILE");

//declaring variables
char buf[BUF_SIZE];  //to store what is read in/written out
int read_test;      //test if EOF
for(;;) {
    read_test = read(0, buf, BUF_SIZE); //read from buffer
    if(read_test == 0) //eof
        break;
    write(wri_inFile, buf, BUF_SIZE);   //write to file

}
close(wri_inFile);
exit(0);
}

Answer 1

您不检查（并使用）读取数据长度。因此，您的数据会被垃圾填充。

应该读取实际数据字节（read_test）：

read_test = read(0, buf, BUF_SIZE); //read from buffer
if(read_test == 0) //eof
    break;
write(wri_inFile, buf, BUF_SIZE);   //write to file
-----------------------^^^^^^^^

这同样适用于另一个孩子。您还应该检查错误条件。

diff cmd，二进制文件x和y不同

1 个答案: