Writing in a C++ matrix

Question

I am studying and implementing some C++ schemes but it is causing errors when assigning value to the matrix. Well... I have a txt file that contains lines with "[email protected]" content. My Ret variable is returning the values correctly, but at the time of inserting in the vector the following error is popped:

Exception generated in 0x0F6DE559 (ucrtbased.dll) in Consoleapplication3.exe: 0xC0000005: breach of access when writing in local 0xCCCCCC.

Debugging the code, all values are apparently correct, but the exception is thrown anyway. I previously tried to do the same process without strcpy, inserting directly into the desired index and using Strtok to separate the string, but the value of all index was changed to the last record always. Could someone give me a light to understand where I’m going wrong?

FILE *fp = NULL;

fp = fopen("Emails.txt", "rt");

char* matriz[99][2];

int index = 0;
char str[256];
char nome[20];
char email[60];

while (1)
{
    char *ret = fgets((char*)str, 255, fp);

    if (ret == NULL)
        break;

    sscanf(str, "%s %s", &nome, &email);

    strcpy(matriz[index][0], nome); // Acusa erro aqui!
    strcpy(matriz[index][1], email);

    index++;
};

Answer 1

I was wondering if you are using C or C++, why the question speaks C++ and the code is in C.

I did here an example of how to read a file using C++.

Suppose your Emails.txt file is as follows:

nome1 [email protected]
nome2 [email protected]
nome3 [email protected]
nome4 [email protected]
nome5 [email protected]

main.cpp

#include <iostream>
#include <fstream>
#include <string>
#include <map>

int main() {
  std::string filename = "Emails.txt";

  // Abre o arquivo.
  std::ifstream infile(filename);

  std::map<std::string, std::string> lines;

  if(infile.is_open()){
    std::string name, email;

    // Ler o arquivo linha por linha.
    while(infile >> name >> email) {
      lines[name] = email;
    }
  }else{
    std::cerr << "Não foi possível abrir o seguinte arquivo: " << filename << std::endl;
  }

  // Fecha o arquivo.
  infile.close();

  // Exibe a lista.
  for(auto const& line : lines) {
    std::cout << line.first << " " << line.second << std::endl;
  }

  return 0;
}

Answer 2

There is no need to use a bi-dimensional matrix for this case. It is much easier to understand (and more natural) using a vector of structures. Much less necessary is the use of a two-dimensional array of pointers!! This knots anyone in the head.

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

typedef struct Pessoa
{
  char nome[20];
  char email[60];
} Pessoa;

int main(void)
{
  char str[256];
  Pessoa pessoas[100];
  int i, nPessoas = 0;

  FILE* fp = fopen("emails.txt", "r");
  if (fp == NULL)
  {
    printf("* erro na abertura do arquivo\n");
    exit(1);
  }

  printf("*\n");

  while (nPessoas < 100)
  {
    if (fgets((char*)str, 255, fp) == NULL)
    {
      printf("* fim de arquivo\n");
      break;
    }

    if (sscanf(str, "%19s%59s", pessoas[nPessoas].nome, pessoas[nPessoas].email) != 2)
    {
      printf("* erro, linha mal formatada\n");
      printf("*\n");
      continue;
    }

    nPessoas++;
  }

  printf("*\n");
  printf("* numero de pessoas: %d\n", nPessoas);
  printf("*\n");

  for (i = 0; i < nPessoas; i++)
  {
    printf("* pessoa %d\n", i);
    printf("*   nome:[%s]\n", pessoas[i].nome);
    printf("*   email:[%s]\n", pessoas[i].email);
  }

  printf("*\n");
}