CODEWITHSUNDEEP
cwhile-loopscanfc89
Ted Jenkins
Ted Jenkins

Reputation: 15

How to get a scanf loop to terminate when it reaches the end of file?

I am trying to read in words separated by white space. There are an unknown number of words and there will be multiple lines of input. I want to read in two words at a time and then compare them before moving on.

Right now the reading and comparison work well, but I have not managed to find a way to get the loop to exit once it has reached the end of file and it continues to prompt for new input.

int main() {

char entry1[256];
char entry2[256];

printf("Enter some test words: \n");

while(scanf("%257[^ \t\n]%*c", entry1)){
    printf("compare 1: %s \n", entry1);

    scanf("%257[^ \t\n]%*c", entry2);
    printf("compare 2: %s \n", entry2);

    if ((anagramCheck(entry1, entry2)) == 1) 
        printf("\nThese two words are anagrams.\n");
    else
        printf("\nThese two words are not anagrams.\n");
}
}

This is what I am trying to achieve:

A sample input might be: 

table george creative reactive tabloid pipe

And the output would be:

compare 1: table
compare 2: george

These two words are not anagrams.

compare 1: creative
compare 2: reactive

These two words are anagrams.

compare 1: tabloid
compare 2: pipe

These two words are not anagrams.

Note: -I am compiling in c89. -I did not include anagramCheck since I didn't think it was relevant to my question. But I can edit and include if it happens to be.

Upvotes: 0

Views: 233

Answers (1)

rici
rici

Reputation: 241671

The usual idiom would be

while (scanf("%255s%255s", entry1, entry") == 2) {
  printf("Compare 1: %s\nCompare 2: %s\n", entry1, entry");
  // ...
}

which will stop when it is unable to read two words. It's not clear to me what you are hoping to accomplish with that much more complicated scanf pattern which you couldn't accomplish just with %s. (I changed your 257 to 255, since that is the maximum number of characters you can fit in a 256-byte char array.)

Note that scanf returns EOF (normally -1) on error, and that is a true value as far as C is concerned. It is almost never a good idea to use while (scanf(...)) { ... }, since that will cause the loop to continue on error or end-of-file.

From man scanf on a Linux system:

These functions return the number of input items successfully matched and assigned, which can be fewer than provided for, or even zero in the event of an early matching failure.

The value EOF is returned if the end of input is reached before either the first successful conversion or a matching failure occurs. EOF is also returned if a read error occurs, in which case the error indicator for the stream is set, and errno is set indicate the error.

Upvotes: 1

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