从 CSV 文件填充双指针矩阵

Question

我想用 CSV 中的值填充双指针二维数组。我不想在填充之前读取 csv 文件来获取数组的大小，我想用指针而不是 std::vector 来完成它。我当前的代码是这样的

std::pair<int, int> readFile(const std::string &filename, int **matrix) {
  std::fstream file{filename, std::ios::in};
  if (file.is_open()) {
    std::string line{};
    int col{0};
    int row{0};
    while (std::getline(file, line)) {
      // Check how many cols there are
      int len = std::count(begin(line), end(line), ',') + 1;
      // Allocate a vector with size the cols found before
      int *tmp = reinterpret_cast<int *>(calloc(len, sizeof(int)));
      col = 0;
      // Fill the temp vector with the read numbers
      while (line.size() > 0) {
        int num{-1};
        // This is just to parse a number, nothing special here
        if (line.find(",") != std::string::npos) {
          num = std::stoi(line.substr(0, line.find(",")));
          line.erase(0, line.find(",") + 1); // +1 to also delete delimiter
        } else {
          num = std::stoi(line);
          line = ""; // Set line empty to go out of the while
        }
        tmp[col] = num;
        col++;
      }
      // Assign the temporal vector to a row of the matrix
      matrix[row] = tmp;
      row++;
    }
    return {row, col};
  }
  std::cout << "Failed to open file at " << filename << std::endl;
  return {-1, -1};
}

int main() {
  int **matrix;
  auto shape = readFile("file.csv", matrix);
  for (size_t row = 0; row < shape.first; row++) {
    for (size_t col = 0; col < shape.second; col++) {
      std::cout << matrix[row][col] << " ";
    }
    std::cout << std::endl;
  }
  // Free the pointers
  for (size_t row = 0; row < shape.first; row++) {
    free(matrix[row]);
  }
}

我目前的结果是：

0 0 -751362032 21853 1 
2 3 4 2 3 
2 1 3 4 5 
3 2 1 4 3 
2 2 2 2 2 
free(): double free detected in tcache 2
Aborted (core dumped)

似乎在打印之前释放了第一个 tmp 向量（其余值是正确的）。知道我错过了什么吗？

Answer 1

您将 matrix 传递给未初始化的 readFile 函数，然后继续使用 matrix[i]=tmp 访问它。这可能会导致各种问题，因为您正在使用不属于您的内存。

从 CSV 文件填充双指针矩阵

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