c - fscanf 在末尾扫描一个额外的字符

Question

它总是在末尾打印一个额外的字符。这是代码:

#include <stdio.h>

int main ()
{
    char bit;
    FILE *fp_read,*fp_write;
    fp_read = fopen("test.txt","r");

    if(fp_read==NULL) {
        printf("Error!! Unable to open the file!!");
        return 1;
    }
    while(!feof(fp_read)) {
        fscanf(fp_read,"%c",&bit);
        printf("%c",bit);
    }
    fclose(fp_read);

    return 0;
}

如果 test.txt 包含 010101，它会打印 0101011。如果 00110 则打印 001100。如果它包含 abc 则打印 abcc 。这意味着它总是重复最后一个字符。

问题是什么？谁能解释一下？

Answer 1

我无法重现错误。

请参阅 David Bowling 在原帖中的第一条评论以获得简洁的解释。

cppreference page for feof有一个较短的版本。

The eof function only reports the stream state as reported by the most recent I/O operation, it does not examine the associated data source. For example, if the most recent I/O was a fgetc, which returned the last byte of a file, feof returns zero. The next fgetc fails and changes the stream state to end-of-file. Only then feof returns non-zero. In typical usage, input stream processing stops on any error; feof and ferror are then used to distinguish between different error conditions.

这意味着在while循环中使用feof可能并不合适。文件的最后一个字符可能是垃圾字符，并且在不同系统中会有所不同。

尝试这样做。

while(fscanf(fp_read,"%c",&bit) != EOF) {        
    printf("%c",bit);
}