Weird characters in output

Question

I have this program that extracts book data(title, isbn, authors and publisher) from a file and then populates 3 structs. The structs are all correctly populated and the command "t" that prints all the books alphabetically in order is working correctly. So everything up until that point works but then if I try to use the "i 'isbn'" (ex.: i 9780321942050) command it doesn't work. It prints some weird characters and I've tried everything in the range of function of my brain to try and fix it but nothing worked. From what I could understand the problem is in the vecRefSearchIsbn function and what it returns because everything is being passed correctly up until that point. I don't have that much knowledge about pointers so I may be missing something but I've tried a lot of things so I'm not going to list them all. I provided the main function and the vecRefSearchIsbn function because that is where I think the problem resides but if someones thinks that the problem is elsewhere I won't hesitate to provide any other functions.

This is what I get in the output:

Digite um comando (t, i + isbn, q): i 9780321942050

Title:p▬┼%7☻
ISBN: 0z┼%7☻
Authors: ░É┼%7☻
Publisher: `¡┼%7☻

typedef struct {
 char *title;
 char isbn[MAX_ISBN];
 char *authors;
 char *publisher;
} Book;
typedef struct{
 Book **refs;
 int size;
 int space;
} VecBookRef;
typedef struct{
 VecBookRef *titleVec;
 VecBookRef *isbnVec;
} DynCollection; 

#include <stdio.h>
#include <stdlib.h>
#include "vector.h"
#include "book.h"
#include "collection.h"
#include "splitfield.h"


int main(){
    char input[100];
    DynCollection *col;

    FILE *f=fopen("dados.csv", "r");
    if(f==NULL){
        printf("Erro ao abrir ficheiro");
        return 0;
    }
    vecRefCreate();
    col=collecBuild(f);
    if(col==NULL){
        printf("Erro ao criar coleção");
        return 0;
    }
    fclose(f);

    do{
        printf("\nDigite um comando (t, i + isbn, q): ");
        fgets(input, sizeof(input), stdin);
        int inputLen=strlen(input);

        if(inputLen==2 && input[0]=='t'){
            vecRefScan(col->titleVec, NULL, printBook);
        }
        else if(inputLen>2 && input[0]=='i' && input[1]==' '){ 
            char isbn[MAX_ISBN];
            sscanf(input+2, "%s", isbn);
            if(strlen(isbn)!=13){
                printf("\nISBN invalido\n");
                continue;
            }
            Book *b=vecRefSearchIsbn(col->isbnVec, isbn);
            if(b!=NULL){
                printBook(b, NULL);
            }else{
                printf("\nNao foi encontrado um livro com o ISBN inserido\n");
                continue;
            }
        }
        if(inputLen==2 && input[0]=='q'){
            collecFree(col);
            printf("Memoria limpa");
        }
    }while(input[0]!='q');

    return 0;
}

Book *vecRefSearchIsbn(VecBookRef *vec, char *isbn){

int comparator(const void *key, const void *book){
    const char *isbn=(const char *)key;
    const Book *b=*(const Book **)book;
    return strcmp(isbn, b->isbn);
}
Book *b=(Book*)bsearch(isbn, vec->refs, vec->size, sizeof(Book *), comparator);
if(b!=NULL){
    return b;
}else return NULL;

}

void printBook(Book *b, void *context){
    printf("\nTitle:%s\nISBN: %s\nAuthors: %s\nPublisher: %s\n", b->title, b->isbn, b->authors, b->publisher);
}

Answer 1

Always use a maximum field width when reading a string with *scanf() as this will cause a buffer overflow if user enters too much data. It's too late to check after the fact:

            char isbn[MAX_ISBN];
            sscanf(input+2, "%s", isbn);
            if(strlen(isbn)!=13){

Otherwise the corruption/error is in code you haven't shown us. I made the following changes:

1. Changed MAX_ISBN from 14 to 13 (required for the str() macro).
2. Changed isbn definition to use MAX_ISBN+1.
3. Define INPUT_LEN instead of the magic number 100 inline.
4. (Not fixed) Check if fgets() returns NULL.
5. Strip the trailing newline from input as you probably don't care about it. If you do then you check that overflow is \n.
6. Don't call strlen() just use functions that can deal with input that is possible too small, i.e. strcmp(), strncmp(). That said, I might be tempted to switch on input[0] even if means you now need to use a goto to exit the loop instead of the break.
7. Changed error handling for too large a isbn, and used a maximum field width to read it.
8. Use break/goto instead of testing the exit condition twice.

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

#define MAX_ISBN 13
#define INPUT_LEN 100
#define str(s) str2(s)
#define str2(s) #s

typedef struct {
    char *title;
    char isbn[MAX_ISBN+1];
    char *authors;
    char *publisher;
} Book;

int main(void) {
    char input[INPUT_LEN];
    for(;;) {
        printf("\nDigite um comando (t, i + isbn, q): ");

        fgets(input, sizeof(input), stdin);
        input[strcspn(input, "\n")] = '\0';
        if(!strncmp(input, "i ", 2)) {
            char isbn[MAX_ISBN+1];
            char overflow;
            if(sscanf(input+2, "%" str(MAX_ISBN) "s%c", isbn, &overflow) != 1) {
                printf("\nISBN invalido\n");
                continue;
            }
            printf("%s\n", isbn);
        } else if(!strcmp(input, "q")) {
            printf("Memoria limpa");
            break;
        }
    }
}

and example session:

Digite um comando (t, i + isbn, q): i 9780321942050
9780321942050

Digite um comando (t, i + isbn, q): i 9780321942050x

ISBN invalido

Digite um comando (t, i + isbn, q): q