问题
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;
}
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 contains a space separated list of characters like: a b c d e f
回答1:
This will not work the way you expect:
while((c=fscanf(fp,"%c",&c))!=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.
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).
You should try this instead:
while(fscanf(fp,"%c",&c) == 1)
Or:
while(fscanf(fp,"%c",&c) != EOF)
Which is equivalent to saying "As long as there is a character to read..."
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
.
来源:https://stackoverflow.com/questions/21645857/difference-between-getc-and-fscanf