getc和fscanf之间的区别 [英] difference between getc and fscanf

问题描述

为什么以下代码能正常工作:

why does the following code work fine:

#include<stdio.h>
int main()
{
     FILE *fp=fopen("input.txt","r+");
     char c;
     while((c=getc(fp))!=EOF)
     {
         printf("%c",c);
     }
     fclose(fp);
     return 0;
}

但是此代码给出了错误分段错误，核心已转储":

but this code gives an error 'segmentation fault, core dumped':

#include<stdio.h>
int main()
{
     FILE *fp=fopen("input.txt","r+");
     char c;
     while((c=fscanf(fp,"%c",&c))!=EOF)
     {
         printf("%c",c);
     }
     fclose(fp);
     return 0;
}

input.txt包含空格分隔的字符列表，例如:a b c d e f

input.txt contains a space separated list of characters like: a b c d e f

推荐答案

这将无法按您期望的方式工作:

This will not work the way you expect:

while((c=fscanf(fp,"%c",&c))!=EOF)

getc()返回读取的字符，可以是EOF，但是fscanf()返回分配的输入项数，如果在进行任何转换之前发生故障，则返回EOF.

getc() returns the character read, which can be EOF, but fscanf() returns the number of input items assigned, or EOF if there was a failure before any conversion took place.

您不能将此返回值分配给c，因为该返回值不是读取的字符(然后您尝试稍后打印).

You can't assign this return value to c, because the return value is not the character read (which you then try to print later).

您应该尝试以下操作:

while(fscanf(fp,"%c",&c) == 1)

或者:

while(fscanf(fp,"%c",&c) != EOF)

这相当于说只要有一个要读的字符..."

Which is equivalent to saying "As long as there is a character to read..."

此外，在第一种情况(使用getc()的代码)中，c应该为int-如果目标平台使用无符号字符，则可以有一个无限循环，因为c将始终转换为一个正整数(同样，仅在具有未签名字符的平台中)，因此永远不会等于EOF.如果查看getc()和putc()的手册页(以及其他处理字符的功能)，您会发现它们收到的是int，而不是char.

Also, in the first case (the code where you use getc()), c should be int - you can have an infinite loop if the target platform uses unsigned chars, because c will always be converted to a positive int (again, only in platforms with unsigned chars), and thus will never be equal to EOF. If you check the manpages for getc() and putc() (and other functions that deal with a character), you will see that they receive int, not char.

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