fgets or strtok error returning unwanted third line

Question

I had the following code to try and get 2 values for 2 different players, however this code is causing an unwanted third line to appear as shown below.

for(int i = 0; i < 6; i++){
    printf("Player %c>", player);
    fgets(move, 4, stdin);
    y_coord = strtok(move, sp);
    x_coord = strtok(NULL, sp);


    printf("You entered: %s, %s\n", x_coord, y_coord);
    if(player == 'O'){
        player = 'X';
    }
    else{
        player = 'O';
    }
}

output:

Player O>5 5
You entered: 5, 5
Player X>You entered: (null),

Player O>^C

score 1 · Accepted Answer · answered Aug 18 '16 at 14:28

1

The problem is that you read only three characters, which leaves the newline in the input buffer.

The size passed to fgets must include the terminating '\0' character, so to have fgets read the newline as well you need a buffer size of 5 character, i.e.

char move[5];  // Two characters separated by space, plus newline and terminator
...
fgets(move, sizeof(move), stdin);

answered Aug 18 '16 at 14:28

Some programmer dude

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that works but now it copies in a \n as well. any ways to remove that? – Altern8 Aug 18 '16 at 14:33
@Altern8 Yes there are ways to remove it. If it exists in the string, it will always be a position `strlen(move) - 1`. Check for it there. Also remember that a good way to remove the last character is to change it to the terminator character `'\0'`. – Some programmer dude Aug 18 '16 at 14:38
@Altern8 See [Removing trailing newline character from fgets() input](http://stackoverflow.com/q/2693776/2410359) – chux - Reinstate Monica Aug 18 '16 at 16:04
1

Checking `strlen(move) - 1` sets up for an exploit - rare, but `move[0]` may be 0. – chux - Reinstate Monica Aug 18 '16 at 16:06

fgets or strtok error returning unwanted third line

1 Answers1