fgets inside the while loop

Question

I'm having an issue with fgets because it is returning \\n on the first time it enters the while loop right after the k input. Since I'm already inside the while loop and my #1 try as already been written, how do I deal with this?

int main() {
    char r;

    printf("How to input?\n");
    printf("Keyboard ([K])\n File ([F])\n Leave ([E])\n");
    scanf("%c", &r);

    if (r == 'k' || r == 'K') {
        printf("\nKeyboard\n");
        opcaoTeclado();
    } else {
       // stuff
    }
}

void opcaoTeclado() {
    int try = 0;
    char inputline[161];

    while (try <= 10) {
        printf("\n#%d try\n ", try);
        fgets(inputline, 160, stdin);
        try++;
    }
}

Answer 1

After the call to scanf() , there's a newline in the input which is read by the first call fgets() . fgets() stops reading input when it encounters a newline \\n . Hence, it doesn't read any input.

Add a call to getchar(); right after scanf() to consume the newline.

Or you can also use a loop to consume if there are multiple chars in the input.

int c;

while((c= getchar()) != '\n' && c != EOF); 

In general, it's best to avoid mixing scanf() with fgets() . You can use fgets() instead of scanf() and parse the line using sscanf() which is less prone.

Answer 2

You should clean stdin's buffer. You can do it using fflush(stdin); before your loop. But it's a bad style. Consider also fseek(stdin,0,SEEK_END); .

Answer 3

您只需在格式后添加空格即可使用\\n

scanf("%c ", &r);

Answer 4

1. I'm having an issue with fgets because it is returning \\n on the first time it enters the while loop right after the "k" input.

   That's because for scanf("%c", &r); when you enter k[ENTER_KEY] , the character k gets stored in variable r leaving the \\n (ENTER key pressed) in the stdin stream.

   So for fgets(inputline, 160, stdin); , it finds the \\n newline character in stdin , stoes it in inputline and exits as from man -s3 fgets :

   fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer.

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2. Since I'm already inside the while loop and my "#1 try" as already been written, how do I deal with this?

   You can consume that \\n in stdin by using getchar()