Finding whether a substring exists in a string using user input from STDIN

Question

I have a simply task that I wish to do here is the workflow

User inputs a string which he/she wishes to search exits in a text file
If string is found, code then prints all the lines in a text file where that string exists.
Code terminates/function ends.

Now I managed to get file reading working and all, but the issue happens when I combine user input.

For example, when the user inputs "sushi" it does not print out the lines of string in the text file where the word "sushi" exists.

But if I pass the term manually, it works fine (i.e strstr(lineOfText,"sushi));

Here is my code, what could the issue be

int main() {
    word_search();
    return 0;
}

int word_search() {
    FILE *textFile;
    char line[MAX_LINE_LENGTH];

    textFile = fopen("PATH TO TEXT FILE", "r");

    if (textFile == NULL) {
        return 1;
    }
    printf("Please input word to search:");
    char userInput[] = "";
    fgets(userInput, 250, stdin);

    while (fgets(line, MAX_LINE_LENGTH, textFile)) {
        if (strstr(line, userInput) != NULL) {
            printf("%s", line);
        }
    }

    fclose(textFile);
    return 0;
}

Contents of file

1 Wallaby Way Fenwick
1 Sushi Way Fenwick
1 Wallaby Sushi Way Fenwick
1 Alexandria Way Fenwick
1 Alexandira Sushi Ashfield Way Fenwick

C doesn't have a string class. The string class which C does not have is not char. You need to study how arrays work before using strings. Here's a newbie FAQ: Common string handling pitfalls in C programming — Lundin
– Lundin, Commented Feb 7, 2023 at 7:23
fgets(), reading from stdin leaves the '\n' on the end of the string. You won't find "Way", either, but will have success with "Fenwick" from the keyboard because that will be "Fenwick\n" in the buffer... line[ strcspn( line, "\n" ) ] = '\0'; will fix your problem... (PS: That's a very peculiar filename.) (PPS: "sushi" will not match "Sushi"... Details matter...) — user17592432
– user17592432, Commented Feb 7, 2023 at 7:27

Oka · Accepted Answer · 2023-02-07 07:43:31Z

The following

char userInput[] = "";

defines userInput to be an array of size 1. A buffer of size 1 can only hold the empty string.

Attempting to fill this buffer

fgets(userInput,250,stdin);

with up to 250 bytes will surely invoke Undefined Behaviour.

When a newline character is encountered, fgets stores it in the buffer (unless doing so would not leave room for the null-terminating byte).

You must remove the newline character from the query string. See: Removing trailing newline character from fgets() input.

An example program:

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

int main(int argc, char **argv) {
    if (argc < 2) {
        fprintf(stderr, "usage: %s FILENAME\n", *argv);
        return EXIT_FAILURE;
    }

    char needle[512];

    printf("Enter a string to search for: ");

    if (!fgets(needle, sizeof needle, stdin)) {
        if (ferror(stdin))
            perror("reading stdin");
        return EXIT_FAILURE;
    }

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

    FILE *file = fopen(argv[1], "r");

    if (!file) {
        perror(argv[1]);
        return EXIT_FAILURE;
    }

    char line[1024];

    while (fgets(line, sizeof line, file))
        if (strstr(line, needle))
            printf("%s", line);

    fclose(file);
}

Running this program on its own source:

$ ./a.out find.c
Enter a string to search for: need
    char needle[512];
    if (!fgets(needle, sizeof needle, stdin)) {
    needle[strcspn(needle, "\n")] = '\0';
        if (strstr(line, needle))

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