尝试使用文件 i/o 读取和写入来查找两个文件不同的字节位置

Question

我正在尝试使用读写命令比较两个文件以找出它们的不同之处，并且在某种意义上我要离开一本书的示例，并认为我的比较功能是正确的，但我显然没有，因为 sprintf功能打印出来。我最好的猜测是我如何比较这两个文件？：

（更新代码）

 Byte pos where two files differ is:
 Byte value of file 1:  %o
 Byte value of file 2: %o

 void compare_two_binary_files(int f1, int f2)
 {
      write(1, sprintf, 10);
      ssize_t byte_read_f1, byte_read_f2, length, numRead, bob;
      char buf1[BUF_SIZE], buf2[BUF_SIZE], a[100], b[100], counter[100];
      int count = 0, b_pos1, b_pos2;
      while ((byte_read_f1 = read(f1, buf1, sizeof buf1) > 0) && (byte_read_f2 = read(f2, buf2, sizeof buf2) >0)) {
            ssize_t len =  byte_read_f1 <byte_read_f2 ? byte_read_f1 : byte_read_f2;
            if (memcmp(buf1, buf2, len) != 0){
                 ssize_t i;
                 sprintf(counter, "Byte pos where two files differ is:%lld\n", (long long) count + i);
                 sprintf(a, "Byte value of file 1: %hho\n", buf1[i]);
                 sprintf(b, "Byte value of file 2: %hho\n", buf2[i]);
                 break;
            }
            count += len;
 }

新代码，但由于没有通过 if "!=" 语句仍然出错，因为它根本没有在我想要的时候通过它。请帮忙：

 void compare_two_binary_files(int f1, int f2)
 {
    ssize_t byte_read_f1, byte_read_f2, length, i;
    char buf1[BUF_SIZE], buf2[BUF_SIZE], a[BUF_SIZE], b[100], counter[100];
    int count = 0;
    while ((byte_read_f1 = read(f1, buf1, BUF_SIZE) > 0) && (byte_read_f2 = read(f2, buf2, BUF_SIZE) >0)){
            if (byte_read_f1 != byte_read_f2){
                    sprintf(counter, "Byte pos where two files differ is:%lld\n", (long long)  count + 1);
                    sprintf(a, "Byte value of file 1:  %o\n", buf1[i]);
                    sprintf(b, "Byte value of file 2: %o\n", buf2[i]);
                    write(1, counter, 100);
                    write(1, a, 100);
                    write(1, b, 100);
            }
            i++;
            count++;
    }
 }

我现在在这里。而且它不会进入if (memcmp(buf1, buf2, len) != 0){：

 void compare_two_binary_files(int f1, int f2)
 {
    //write(1, sprintf, 10);
    ssize_t byte_read_f1, byte_read_f2, length, numRead, bob;
    char buf1[BUF_SIZE], buf2[BUF_SIZE], a[100], b[100], counter[100];
    int count = 0, b_pos1, b_pos2, hey;
    while ((byte_read_f1 = read(f1, buf1, sizeof buf1) > 0) && (byte_read_f2 = read(f2, buf2, sizeof buf2) >0)) {
            ssize_t len =  byte_read_f1 <byte_read_f2 ? byte_read_f1 : byte_read_f2;
            if (memcmp(buf1, buf2, len) != 0){
                    ssize_t i;
                    for (i = 0; i<len; i++){
                            if (buf1[i] != buf2[i]) break;
                    }
                    sprintf(counter, "Byte pos where two files differ is:%lld\n", (long long) count + i);
                    write(1, counter, 100);
                    sprintf(a, "Byte value of file 1: %hho\n", buf1[i]);
                    sprintf(b, "Byte value of file 2: %d\n", buf2[i]);
                    write(1, counter, 100);
                    write(1, b, 100);
                    write(1, a, 100);
                    break;
            }
            count += len;
    }
 }

当我将 memcmp 的 != 更改为 == 时，它可以工作，但给了我错误的数字。我应该得到字节位置 4，文件 1 是 65，文件 2 是 143，但是得到 pos 1，文件 1 是 163，文件 2 是 115

Answer 1

需要单独的缓冲区并使用memcmp 和/或循环来比较字节。
所有人都知道文件长度可能不同。

// Untested code
char buf1[BUF_SIZE];
char buf2[BUF_SIZE];
while (((byte_read_f1 = read(f1, buf1, sizeof buf1)) > 0) && 
       ((byte_read_f2 = read(f2, buf2, sizeof buf2)) > 0)) {
  // find min length
  ssize_t len =  byte_read_f1 <byte_read_f2 ? byte_read_f1 : byte_read_f2;
  if (memcmp(buf1, buf2, len) != 0) {  // use memcmp for speed
    ssize_t i;
    for (i = 0; i<len; i++) {
      if (buf1[i] != buf2[i]) break;
    } 
    sprintf(counter, "Byte pos where two files differ is:%lld\n", (long long) count + i);
    sprintf(a, "Byte value of file 1: %hho\n", buf1[i]);
    sprintf(b, "Byte value of file 2: %hho\n", buf2[i]);
    break;
  }
  count += len;
  // If lengths differ
  if (byte_read_f1 != byte_read_f2) {
    sprintf(counter, "Byte pos where two files differ in length: %lld\n", (long long) count);
    // TBD code for a and b
    break;
    }
}