Problems with fgets function-CodePudding

Here I use fgets() to get user input with several strings, it never appeared in the output:

#include <stdio.h>

int main() {
    char color[20];
    char pluraNoun[20];
    char celebrity[20];

    printf("Enter a color: ");
    scanf("%s", color);
    printf("Enter a plural noun: ");
    scanf("%s", pluraNoun);
    printf("Enter a celebrity: ");

    fgets(celebrity, 20, stdin);

    printf("Roses are %s\n", color);
    printf("%s are blue\n", pluraNoun);
    printf("I love %s\n", celebrity);
    return 0;
}

CodePudding user response：

scanf() with a specified width for string is same as fgets(), but fgets() reads a extra character namely newline, which adds extra code to remove them.

I would suggest you to keep using scanf() with width for strings.

Some Points

Initialize your character arrays using = { };
Always check whether scanf() was successful or not
Make sure those character arrays have an extra space for null terminating character '\0'

Final Code

#include <stdio.h>

int main() {
    char color[21] = {};
    char pluraNoun[21] = {};
    char celebrity[21] = {};

    printf("Enter a color: ");
    if (scanf(" s", color) != 1) {
        fputs("bad input", stderr);
    }

    printf("Enter a plural noun: ");
    if (scanf(" s", pluraNoun) != 1) {
        fputs("bad input", stderr);
    }

    printf("Enter a celebrity: ");
    if (scanf(" s", celebrity) != 1) {
        fputs("bad input", stderr);
    }

    printf("Roses are %s\n", color);
    printf("%s are blue\n", pluraNoun);
    printf("I love %s\n", celebrity);
    return 0;
}

CodePudding user response：

Don't mix scanf() and fgets() or as man page says:

It is not advisable to mix calls to input functions from the stdio library with low-level calls to read(2) for the file descriptor associated with the input stream; the results will be undefined and very probably not what you want.

Here is a fgets() version:

#include <stdio.h>
#include <string.h>

#define LEN 20

void strip(char *s) {
    size_t n = strlen(s);
    if(n && s[n-1] == '\n') s[n-1] = '\0';
}

int main() {
    char color[LEN];
    char pluraNoun[LEN];
    char celebrity[LEN];

    printf("Enter a color: ");
    fgets(color, LEN, stdin);
    strip(color);

    printf("Enter a plural noun: ");
    fgets(pluraNoun, LEN, stdin);
    strip(pluraNoun);

    printf("Enter a celebrity: ");
    fgets(celebrity, LEN, stdin);

    printf("Roses are %s\n", color);
    printf("%s are blue\n", pluraNoun);
    printf("I love %s\n", celebrity);
    return 0;
}

I left it out to not change your program too much, but check the return value from fgets() if you want to ensure your program does something sensible if on EOF.