c - 尝试打印文件中的字符但打印空白

Question

这是我的一个小方法:

void CompareTwoFiles(FILE *fp1, FILE *fp2){

char ch1, ch2;
int flag = 0;
//must seek first to determine the sizes
fseek (fp1, 0, SEEK_END);
fseek (fp2, 0, SEEK_END);
if(ftell(fp1) != ftell(fp2)){
    printf("The sizes of the files are different so they cannot be equal.\n");
    return;
}
while (((ch1 = fgetc(fp1)) != EOF) &&((ch2 = fgetc(fp2)) != EOF))
{
    /*
      * character by character comparision
      * if equal then continue by comparing till the end of the files
      */
    if (ch1 == ch2)
    {
        flag = 1;
        continue;
    }     
    //If not equal then return the byte position         
    else
    {
        fseek(fp1, -1, SEEK_CUR);        
        flag = 0;
        break;
    }
}

if (flag == 0)
{
    printf("Two files are not equal :  byte position at which two files differ is %d.\n", ftell(fp1)+1);
    printf("First file contains %c and second file contains %c \n", ch1, ch2); //ISSUE: prints blank for ch1 and ch2
}
else
{
    printf("Two files are Equal\n ", ftell(fp1)+1);
}

}

我只想在我的 printf 中打印我用 fgetc 分配的两个字符。但是我却一片空白。输出如下所示:

第一个文件包含，第二个文件包含

有人可以指出我哪里出了问题吗？我对 C 和 C++ 有点生疏。

Answer 1

首先修复警告。

$ gcc main.c 
main.c: In function ‘CompareTwoFiles’:
main.c:37:12: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long int’ [-Wformat=]
     printf("Two files are not equal :  byte position at which two files differ 
            ^
main.c:42:12: warning: too many arguments for format [-Wformat-extra-args]
     printf("Two files are Equal\n ", ftell(fp1)+1);

进行干净的编译并倒带文件，您会看到您的代码有效。您的代码没有倒带，因此您不知道得到的是哪个 char。

#include <stdio.h>

void CompareTwoFiles(FILE *fp1, FILE *fp2) {

    char ch1, ch2;
    int flag = 0;
//must seek first to determine the sizes
    fseek(fp1, 0, SEEK_END);
    fseek(fp2, 0, SEEK_END);
    if (ftell(fp1) != ftell(fp2)) {
        printf("The sizes of the files are different so they cannot be equal.\n");
        return;
    }
    rewind(fp1);
    rewind(fp2);
    while (((ch1 = fgetc(fp1)) != EOF) && ((ch2 = fgetc(fp2)) != EOF)) {
        /*
          * character by character comparision
          * if equal then continue by comparing till the end of the files
          */
        if (ch1 == ch2) {
            flag = 1;
            continue;
        }
            //If not equal then return the byte position
        else {
            fseek(fp1, -1, SEEK_CUR);
            flag = 0;
            break;
        }
    }

    if (flag == 0) {
        printf("Two files are not equal :  byte position at which two files differ is %d.\n", (int) ftell(fp1) + 1);
        printf("First file contains %c and second file contains %c \n", ch1, ch2); //ISSUE: prints blank for ch1 and ch2
    }
    else {
        printf("Two files are Equal %d\n ", (int) ftell(fp1) + 1);
    }

}


int main() {

    FILE *fp;
    fp = fopen("tmp.txt", "r");
    FILE *fp2;
    fp2 = fopen("tmp2.txt", "r");

    CompareTwoFiles(fp, fp2);
    return 0;
}

tmp.txt

1 1 23 2134 123 12321

123

42

tmp2.txt

0 1 23 2134 123 12321

123

42

输出

$ ./a.out 
Two files are not equal :  byte position at which two files differ is 1.
First file contains 1 and second file contains 0