fgets segmentation fault reading from stdin

Question

I'm currently trying to read a line from stdin using fgets() but i'm getting a segmentation fault (i'm not geting the segmentation fault anymore, please see edit)

int main(void)
{
    char selection;
    string firstName = NULL;

    printf("[A]dd a new client \n");
    printf("[D]isplay all clients \n");
    printf("[I]ncome Average for all clients \n");
    printf("[Q]uit \n");  

    selection = fgetc(stdin);
    printf("\n");

    switch (selection) {
    case 'A':
        printf("First name: ");
        fgets(firstName, MAXNAMESIZE, stdin);
        printf("\n");

        ...
    }
}

This is the compiler's output:

[A]dd a new client 
[D]isplay all clients 
[I]ncome Average for all clients 
[Q]uit 
A

First name: Segmentation fault

Thank you!!

Edit:

i've changed the code like this:

int main(void)
{
    char selection;
    string firstName;

    printf("[A]dd a new client \n");
    printf("[D]isplay all clients \n");
    printf("[I]ncome Average for all clients \n");
    printf("[Q]uit \n");  

    selection = fgetc(stdin);
    printf("\n");

    switch (selection) {
        case 'A':
            if ((firstName = malloc(MAXNAMESIZE * sizeof(char))) == NULL)
                return 1;
            printf("First name: ");
            fgets(firstName, MAXNAMESIZE, stdin);
            printf("\n");

        ...
    }
}

But now i'm not able to enter any name, the program just ends. This is the output:

~/workspace/ $ ./test
[A]dd a new client 
[D]isplay all clients 
[I]ncome Average for all clients 
[Q]uit 
A

First name: 
~/workspace/ $

to NULL. i tried using string firstName; and string firstName = " "; but in the first case firstName is uninitialized and in the second i also get a segmentation fault — Santiago Aguilar

Claudio Cortese Claudio Cortese · Accepted Answer · 2018-02-19T00:38:19

You need to malloc firstName before you can use it, hence make sure to #include <stdlib.h>.

Try string firstName = malloc(MAXNAMESIZE * sizeof(char));

Always check that the result of malloc is not NULL.

Moreover, at the end of your program or when you think it's more useful free(firstName) to prevent memory leaks.

fgets segmentation fault reading from stdin

1 Answers