C values of dynamic array wrong

Question

basically in this code im saving content from a txt file to a dynamic array(until then is all good), but when I try to reallocate memory and add more structs some values in the middle get wrong, always the same ones This is the code I used to save to a dynamic array

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#include "header.h"

int iniF(guitarra *vg,int *tamvg)
{
int ch=0, i;

FILE *g;

g = fopen("guitarras.txt", "r"); // abrir ficheiro

if(g == NULL)
{
    printf("Erro ao abrir ficheiro %s", "guitarras.txt");
}

while(!feof(g)) //check how many lines the file have
{
    ch = fgetc(g);
    if(ch == '\n')
    {
        (*tamvg)++;
    }
}

fseek(g, 0, SEEK_SET);

vg = malloc(*tamvg * sizeof(guitarra));

for(i=0; i<*tamvg; i++)
{
    fscanf(g, ("%d %f %f %d %s"), &vg[i].id, &vg[i].pdia, &vg[i].valor, &vg[i].estado, &vg[i].nome );
}

fclose(g);
return vg;
}

and this to reallocate

#include <stdio.h>
#include <stdlib.h>
#include "header.h"

 int addguit(guitarra *vg, int *tamvg)
{

int stop=0;


do
{
    vg = realloc(vg, sizeof(guitarra)); //allocating one size of struct guitarra
    printf("Id: ");
    scanf("%d", &vg[*tamvg].id);
    printf("Preco por dia: ");
    scanf("%f", &vg[*tamvg].pdia);
    printf("Valor: ");
    scanf("%f", &vg[*tamvg].valor);
    printf("Estado: ");
    scanf("%d", &vg[*tamvg].estado);
    printf("Nome: ");
    scanf("%s", &vg[*tamvg].nome);
    printf("Deseja adicionar mais guitarras ao stock? Sim[1] Nao[0]: "); //asking if wants to allocate one more
    scanf("%d", &stop);
    (*tamvg)++;
}
while(stop==1);

return vg;
}

the values are simple " 1 1 1 1 a"; " 2 2 2 2 b", and so on, you get it.

heres a print screen of what im talking about

ptrscr of the problem

Answer 1

Your call to realloc does not add the size of one struct to the array. Instead it resizes it to the size of a single struct (see reference for realloc ). The memory for the rest of the array is no longer reserved and can be claimed/modified by other programs. Assuming that tamvg points to the current length of the array, you should have something similar to the following:

vg = realloc(vg, sizeof(guitarra)*(*tamvg+1));