从C中的结构成员char数组打印char数组时fopen数据损坏

Question

I'm having some kind of weird error where the lastName and phoneNumber char array members of the struct phoneEntry are overwritten when I'm trying to print. The following code is bits and pieces of code that relate to the main part that strikes out.

typedef struct
{
    char firstName[30];
    char lastName[30];
    char phoneNumber[30];
} phoneEntry;

size_t phoneBookSize = 1;
phoneEntry* ptrPhoneBook = malloc(phoneBookSize * sizeof(phoneEntry));


FILE *loadedFile;
char fileName[30];
scanf("%s", fileName);
loadedFile = fopen(fileName, "w"); // ERROR OCCURS

fprintf(loadedFile, "First name\tLast name\tPhone Number\n");
int count = 0;
for (count = 0; count < phoneBookSize - 1; count++)
{
    printf("saving %s %s %s\n", ptrPhoneBook[count].firstName, ptrPhoneBook[count].lastName, ptrPhoneBook[count].phoneNumber);
    fprintf(loadedFile, "%s\t%s\t%s\t\n", ptrPhoneBook[count].firstName, ptrPhoneBook[count].lastName, ptrPhoneBook[count].phoneNumber);
}
fclose(loadedFile);

Basically, the data stored in each character array within the struct member is defined and exists until the "loadedFile" initialization. At that point, the data stored in the lastname and phoneNumber char array members within the ptrPhoneBook at index 0 is overwritten with nothing or simply erased.

This is the output:

First name  Last name   Phone Number
James   

As opposed to the expected output:

First name  Last name       Phone Number
James       Bond            007

I can avoid the entire problem by simply starting the count of the ptrPhoneBook at 1 as opposed to 0, but I want to know why fopen corrupts these data members at index 0.

The code I gave probably won't give you an exact output, but the error still exists.

If you would like to try and run the code yourself, here's code that you can run right of the bat.

// Including libraries into the source code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct
{
    char firstName[30];
    char lastName[30];
    char phoneNumber[30];
} phoneEntry;

main()
{

    size_t phoneBookSize = 1;
    phoneEntry* ptrPhoneBook = malloc(phoneBookSize * sizeof(phoneEntry));

    phoneBookSize++;
    phoneEntry* reallocPhoneBook = realloc(ptrPhoneBook, phoneBookSize);

    if (reallocPhoneBook) {
        ptrPhoneBook = reallocPhoneBook;
    } else {
        printf("Failure. Memory error.\n\n");
    }

    strcpy(ptrPhoneBook[0].firstName, "James");
    strcpy(ptrPhoneBook[0].lastName, "Kim");
    strcpy(ptrPhoneBook[0].phoneNumber, "2343");


    FILE *loadedFile;
    char fileName[30];
    scanf("%s", fileName);
    loadedFile = fopen(fileName, "w");

    fprintf(loadedFile, "First name\tLast name\tPhone Number\n");
    int count = 0;
    for (count = 0; count < phoneBookSize - 1; count++)
    {
        printf("saving %s %s %s\n", ptrPhoneBook[count].firstName, ptrPhoneBook[count].lastName, ptrPhoneBook[count].phoneNumber);
        fprintf(loadedFile, "%s\t%s\t%s\t\n", ptrPhoneBook[count].firstName, ptrPhoneBook[count].lastName, ptrPhoneBook[count].phoneNumber);
    }
    fclose(loadedFile);
}

The output for the code above is:

First name  Last name   Phone Number
James   2343    

Answer 1

The realloc is totally bogus, as it allocates 2 bytes instead of 2 phone entries :

size_t phoneBookSize = 1;
/* ... */
phoneBookSize++;
phoneEntry* reallocPhoneBook = realloc(ptrPhoneBook, phoneBookSize);

/* ... */
ptrPhoneBook = reallocPhoneBook;

You probably meant:

realloc(ptrPhoneBook, phoneBookSize * sizeof(phoneEntry))

Answer 2

+1 for cnicutar's answer - the realloc looks like problem 1.

However, your for loop is also wrong: you're looping while count < phoneBookSize - 1 which skips the last entry - change it to count < phoneBookSize eg if phoneBookSize is 3, you should go upto array index [2]