CODEWITHSUNDEEP
ccharfgetsgets
morpheus
morpheus

Reputation: 13

Unable to search character with string input from fgets

I'm writing a program to find the location of a certain character in a string using strchr. When using fgets to input the string from the user, the program does not execute properly.

However when using gets everything works fine.

Code that works using gets():

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

int main() {
    char let;
    char input[50];
    char *ptr;
    printf("what is the string that you would like to check?\n");
    gets(input);
    printf("what is the character that you would like to find?\n");
    let = getchar();
    printf("in string \"%s\"...\n", input);
    ptr = strchr(input, let);
    while (ptr != NULL) {
        printf("the letter %c was found at character %d\n", let, ptr - input + 1);
        ptr = strchr(ptr + 1, let);
    }
    return 0;
}

Output:

what is the string that you would like to check?
what is the character that you would like to find?
in string "why is the world when wondering"...
the letter w was found at character 1
the letter w was found at character 12
the letter w was found at character 18
the letter w was found at character 23

Code that does not work usgin fgets():

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

int main() {
    char let;
    char input[50];
    char *ptr;
    printf("what is the string that you would like to check?\n");
    fgets(input, 16, stdin);
    printf("what is the character that you would like to find?\n");
    let = getchar();
    printf("in string \"%s\"...\n", input);
    ptr = strchr(input, let);
    while (ptr != NULL) {
        printf("the character is found at %d \n", ptr - input + 1);
        ptr = strchr(ptr + 1, let);
    }
    return 0;
}

Output:

what is the string that you would like to check?
what is the character that you would like to find?
in string "abcdefghijklmno"...

Upvotes: 1

Views: 135

Answers (2)

David Collins
David Collins

Reputation: 3032

Change

fgets(input, 16, stdin)

to

fgets(input, sizeof(input), stdin)

When you pass an argument of 16 to fgets() you are instructing it to read no more than 15 characters. Why?

From the fgets() manpage:

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s.

If you provide more than size -1 characters, the remaining characters are left in the input buffer.

Then when the program subsequently calls

let = getchar();

let is assigned whatever the next character in the input buffer is - without even waiting for you to type anything else. It then searches for this character in the string you provided - but in the example you provided doesn't find it.

Upvotes: 2

Vlad from Moscow
Vlad from Moscow

Reputation: 311126

In the first code snippet the call

gets (input);

does not restrict the number of characters the user can input. Take into account that the function gets is not supported by the C Standard and is unsafe.

In the second code snippet you declared the variable input as

char input[50];

So it is more natural to call fgets the following way

fgets (input,sizeof( input ),stdin );

instead of 

fgets (input,16,stdin);

The standard function getchar reads any character including white spaces.

So instead it it is much better to use 

scanf( " %c", &let );

Otherwise getchar can read any character (including for example the new line character) leaved in the input buffer. While the call of scanf will skip any white space character.

Upvotes: 0

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