我scanf（％s，lastName）;时遇到分段错误。 （内部代码）

Question

EDIT: About to try intilizing my chars properly... [didnt work=( ]

EDIT: SOLVED (I can't answer my own question for another 7 hours...)

Thanks for the comment Brian, that's just a constant declared at the top.. (it = 20).

It turns out the error was happening because I forgot to add a next line after I took in the input name.

it's working now =D

:ENDEDIT (lol)

I've code my code below, Basically I put in the first name this is supposed to find

John

Then I put in the last name...

Locke

and as soon as I enter in "Locke" it hits this error, I feel like maybe it's the scanf and I should be using a better alternative ???

int findPatron(struct Library *lib,struct Patron **p)
{
    int i;
    char firstName[NAME_LENGTH], lastName[NAME_LENGTH];
    printf("\nPlease enter the patron's first name: ");
    scanf("%s",firstName);
    printf("\nPlease enter the patron's last name:  "); //this line prints...
    scanf("%s",lastName);  //SEGMENTATION ERROR happens here I'm pretty sure.
    printf("deerrrr");  //this line never prints
     for(i = 0; i<lib->totalPatrons;i++)
    {
            printf("checking %s %s to %s %s",lib->patrons[i].name.first,lib->patrons[i].name.last,firstName,lastName);
            if((strcmp(lib->patrons[i].name.first, firstName) == 0) && (strcmp(lib->patrons[i].name.last, lastName) == 0))
            {
                    **p = lib->patrons[i];
                    return 0;
                    break;
            }
    }

    return 1;  //No Match!
}

Answer 1

You're getting the segmentation fault after your scanf() statements.

If you remove everything after printf("deerrrr"); and add a \\n to that output so the buffer is flushed, you'll find that it all works just fine (provided NAME_LENGTH is at least 6 given your example input).

Part of programming is knowing how to isolate and debug your problems.

Your issues are with your loop and lib struct - you're dereferencing something you shouldn't be.

Answer 2

SEGMENTATION ERROR happens here I'm pretty sure this line never prints

C's printf is buffered, and only gets flushed by an explicit call to fflush or a blocking action (like scanf, which AFAIK flushes stdout as well), so the error could happen in another place. Learn to use debugger, that's the proper way of debugging C programs.