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cstringinputfgetsstrcmp

strcmp on a line read with fgets

I'm trying to compare two strings. One stored in a file, the other retrieved from the user (stdin).

Here is a sample program:

int main()
{
    char targetName[50];
    fgets(targetName,50,stdin);

    char aName[] = "bob";
    printf("%d",strcmp(aName,targetName));

    return 0;
}

In this program, strcmp returns a value of -1 when the input is "bob". Why is this? I thought they should be equal. How can I get it so that they are?

Solution

  • strcmp is one of the few functions that has the reverse results of true and false...if the strings are equal, the result is 0, not 1 as you would think....

    if (strcmp(a, b)) {
    /* Do something here as the strings are not equal */
} else {
    /* Strings are equal */
}

    Speaking of fgets, there is a likelihood that there is a newline attached to the end of the string...you need to get rid of it...

    +-+-+-+--+--+
|b|o|b|\n|\0|
+-+-+-+--+--+

    To get rid of the newline do this. CAVEATS: Do not use "strlen(aName) - 1", because a line returned by fgets may start with the NUL character - thus the index into the buffer becomes -1:

    aName[strcspn(aName, "\n")] = '\0';

+-+-+-+--+
|b|o|b|\0|
+-+-+-+--+

    Now, strcmp should return 0...