i have recently started to learn C and have encountered a little problem with a code snipped.
I want want wo read a character string, 20 chars long, over the stdin, so I have chosen fgets.
Here is my code:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
unsigned int length = 20;
char input_buffer[length];
fgets(input_buffer, length, stdin);
if(input_buffer == NULL)
printf("Error, input too long");
else
printf("%s", input_buffer);
return 0;
}
It compiles without any error, if I enter a sentence shorter than 20 characters, everything is fine. But when I try to test the error handling, it fails.
The output is:
peter@antartica ~/test % ./test
Hello world, this is a very long test
Hello world, this i%
Am I doing anything wrong? I thought fgets returns a NULL pointer if it fails(which should be the case here)?
Thank you for any help.
From fgets reference:
On success, the function returns str.
If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged).
If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).
So it may return NULL without generating an error in the event of reaching end-of-file. You may need to see ferror return value to be sure about it.
Please note fgets() will automatically append a null character (\0) to the end of the string, which may cause the string to be truncated, since you specify how many characters must be read. The call won't fail if a string with more than length characters is found.