diff cmd，二進制文件的x和y不同

Question

我有一個程序需要兩個文件作爲參數。第一個文件將被複制到第二個文件中。該程序分爲兩個孩子，第一個孩子讀取文件並將其通過管道傳遞給另一個孩子，然後另一個孩子將其寫入文件。這兩個文件最終應該是完全相同的。

當我運行DIFF兩個文件我碰到下面的錯誤比較：

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$ 

正如你可以看到他們都是一樣的，但DIFF打印出它們是不同的。顯然，它只是我不瞭解diff cmd。任何幫助，將不勝感激。

我相信由於某些原因，我創建的文件是一個二進制文件，而第一個文件不是，但我不知道爲什麼它是一個二進制文件。我認爲這可能與這行代碼來執行：

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

在這個被寫出到緩衝區，然後我清除緩衝區中的孩子之一。我清除緩衝區是否錯誤？

這裏是貓-e的結果：

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

這裏是CMP的結果：

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

我相信，是我的問題，我怎麼能清除該緩衝區，因此不會把這些扔到底？

所有我的代碼::作者

家長：

#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"); 
} 

兒童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); 
} 

兒童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

你不檢查（和使用）讀取的數據長度。因此，你的數據被填充垃圾。

應該有實際的數據讀取的字節（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 
-----------------------^^^^^^^^ 

這同樣適用於其他孩子。您還應該檢查錯誤情況。