如何检查Unix C中的文件是否相同？(How to check if files are the same in Unix C?)

如何使用Unix C检查一个文件是否与另一个文件相同（具有相同的内容）？我的意思是，当我不能使用fopen, fread, fclose但只是open, read, close ？我对答案表示感兴趣，这些答案显示了如何在Unix C中执行此操作。

我写了一个程序，将一个文件复制到另一个文件，但不知道如何检查它们是否相同：/：

#include <stdio.h> #include <fcntl.h> #include <unistd.h> #include <stdlib.h> int main(int argc, char **argv) { const char *in_filename = "in.txt", *out_filename = "out.txt"; int in_fd, out_fd, bytes_read, bytes_written; int buffsize = 512; char buffer[512]; int success = 0; in_fd = open(in_filename, O_RDONLY); if (in_fd == -1) return -1; out_fd = open(out_filename, O_WRONLY | O_APPEND, S_IRUSR | S_IWUSR); if (out_fd == -1) return -1; for(;;) { bytes_read = read(in_fd, buffer, buffsize); if (bytes_read > 0) { bytes_written = write(out_fd, buffer, bytes_read); if(bytes_written < 0) return -1; } else { if (bytes_read == 0) { if (close(in_fd) < 0) return -1; if (close(out_fd) < 0) return -1; success = 1; break; } else if (bytes_read == -1) { break; return -1; } } } if(success) fprintf(stdout, "%s", "Success!\n"); return 0; }

继承人我试过的：

#include <stdio.h> #include <fcntl.h> #include <unistd.h> #include <stdlib.h> int main(int argc, char **argv) { const char *in_filename = "in.txt", *out_filename = "out.txt"; int in_fd, out_fd, bytes_read_in, bytes_read_out; int buffsize = 512; char in_buffer[512], out_buffer[512]; int the_same = 0; in_fd = open(in_filename, O_RDONLY); if (in_fd == -1) return -1; out_fd = open(out_filename, O_RDONLY); if (out_fd == -1) return -1; for(;;) { bytes_read_in = read(in_fd, in_buffer, buffsize); if (bytes_read_in > 0) { bytes_read_out = read(out_fd, out_buffer, buffsize); if(bytes_read_out > 0) { int i = 0; for(i=0; i<buffsize; i++) { if(in_buffer[i] != out_buffer[i]) the_same = 0; } the_same = 1; } } else { if (bytes_read_in == 0) { if (close(in_fd) < 0) return -1; if (close(out_fd) < 0) return -1; break; } else if (bytes_read_in == -1) { break; return -1; } } } if(the_same) fprintf(stdout, "%s", "Files are the same!\n"); return 0; }

但它显示文件是相同的，而他们不是:(

How to check if one file is the same (has the same content) as the other file using Unix C? I mean, when I cant use fopen, fread, fclose but just open, read, close? I'm interested in answers which shows how to do this ONLY in Unix C.

I wrote a program that copies one file to another but have no idea how to check if they're the same :/ :

Heres what I tried:

#include <stdio.h> #include <fcntl.h> #include <unistd.h> #include <stdlib.h> int main(int argc, char **argv) { const char *in_filename = "in.txt", *out_filename = "out.txt"; int in_fd, out_fd, bytes_read_in, bytes_read_out; int buffsize = 512; char in_buffer[512], out_buffer[512]; int the_same = 0; in_fd = open(in_filename, O_RDONLY); if (in_fd == -1) return -1; out_fd = open(out_filename, O_RDONLY); if (out_fd == -1) return -1; for(;;) { bytes_read_in = read(in_fd, in_buffer, buffsize); if (bytes_read_in > 0) { bytes_read_out = read(out_fd, out_buffer, buffsize); if(bytes_read_out > 0) { int i = 0; for(i=0; i<buffsize; i++) { if(in_buffer[i] != out_buffer[i]) the_same = 0; } the_same = 1; } } else { if (bytes_read_in == 0) { if (close(in_fd) < 0) return -1; if (close(out_fd) < 0) return -1; break; } else if (bytes_read_in == -1) { break; return -1; } } } if(the_same) fprintf(stdout, "%s", "Files are the same!\n"); return 0; }

but it shows that files are the same, while theyre not :(

最满意答案

您只需要同时读取两个缓冲区。例如（也就是说，考虑处理错误），根本不使用C标准库：

#include <fcntl.h> #include <sys/stat.h> #include <sys/types.h> #include <unistd.h> #define BUFFER_SIZE 1024 static int bufcmp(const void *p, const void *q, size_t n) { const char *p1 = p; const char *p2 = q; while (n-- > 0) { if (*p1++ != *p2++) return 0; } return 1; } int main(int argc, char *argv[]) { int fd1 = open(argv[1], O_RDONLY); int fd2 = open(argv[2], O_RDONLY); int same = 1; for (;;) { char buf1[BUFFER_SIZE], buf2[BUFFER_SIZE]; ssize_t n1 = read(fd1, buf1, BUFFER_SIZE); ssize_t n2 = read(fd2, buf2, BUFFER_SIZE); if (n1 < n2) { same = 0; break; } else if (n1 == 0) { break; } else if (bufcmp(buf1, buf2, n1) == 0) { same = 0; break; } } if (same) write(STDOUT_FILENO, "Same content.\n", 14); close(fd1); close(fd2); return 0; }

NB（感谢user4815162342 ）：这段代码并不完全正确。实际上，如果read返回的read字节数小于请求的字节数，则不是错误。但是，为了缩短此代码，我没有包含此管理。

You just have to read two buffers in the same time. For instance (also, think to handle errors), without using C standard library at all:

NB (Thanks to user4815162342): This code is not wholly right. Indeed, it is not an error if the number of bytes read returned by read is smaller than the number of bytes requested. However, to shorten this code, I didn't include this management.

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