Why does my stringstream get filled with garbage after tryng to insert the contents into a vector?-CodePudding

Consider the code:

void someFunc {
    std::stringstream value;
    std::vector<std::vector<int>> mapLayerCollision;
    int row = 0;

    for(int i = 0; i < gid_list.length(); i  ) {
        if(gid_list[i] == ',') {
            value.str("");
            int j = 1;
            while (gid_list[i-j] != ',' and i - j > 0) {
                std::cout << gid_list[i-j] << " | ";
                j  ;
                std::cout << gid_list[i-j] << std::endl;
            }
            j--;
            value.str("");
            std::cout << "j: " << j << std::endl;
            while (j > 0) {
                std::cout << "Inserting: " << gid_list[i-j] << std::endl;
                value << gid_list[i-j];
                std::cout << "Value AFTER: " << value.str() << std::endl;
                j--;
            }
            std::cout << "Putting into vector: " << std::stoi(value.str()) << std::endl;
            //mapLayerCollision[row].push_back(std::stoi(value.str()));
            value.str("");
        }
        
        else if(gid_list[i] == '\n') {
            value.str("");
            int j = 1;
            while (gid_list[i-j] != ',') {
                j  ;
            }
            j--;
            value.str("");
            while (j > 0) {
                value << gid_list[i-j];
                j--;
            }
            std::cout << "Putting into vector: " << value.str() << std::endl;
            //mapLayerCollision[row].push_back(std::stoi(value.str()));
            value.str("");
            row  ;
        }
    }
}

The declaration of gid_list is: std::string gid_list;, and the contents are:

79,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,454,455,70,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,195,210,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,274,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,323,338,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,387,402,0,0,0,0,0,259,
274,0,0,346,0,0,0,350,0,0,0,0,0,0,0,0,0,451,466,0,0,0,0,0,259,
274,0,0,410,0,0,0,414,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
338,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
402,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
338,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,195,210,0,0,0,0,0,0,259,
402,0,0,0,0,195,198,199,200,210,0,0,0,0,0,0,451,466,0,0,0,0,0,0,259,
274,0,0,0,0,387,264,264,264,402,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
274,0,0,0,0,451,455,456,457,466,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
274,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,259,
212,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,216,
73,198,198,198,198,198,198,198,198,198,198,198,198,198,198,198,198,198,199,200,201,199,200,201,76

So I have the lines of code that insert the stringstream value into the vector commented out, the values being printed are correct, but as soon as I uncomment those lines the printed values of the stringstream are garbled and seem to be filled with random stuff. I know that stringstreams can be finicky, but the most confusing part is that the values are printed BEFORE being added to the vector. Question: Why is the stringstream value changing when a line of code is modified AFTER it, and how can I fix it?

CodePudding user response：

I know that stringstream can be finicky

It is not finicky, you use it improperly.

All your code can be simpler

std::vector<std::vector<int>> mapLayerCollision;
std::string line;
while (std::getline(cin, line)) {
  mapLayerCollision.emplace_back();  // This fixes your issue you have asked
  std::istringstream values(line);
  int n;
  while (values >> n) {
    mapLayerCollision.back().push_back(n);
    char c;
    if ((values >> c) && c != ',') {
      // bad content
      break;
    }
  }
}

The issue in your code is mapLayerCollision[row] that attempts to access rowth element of the empty vector.

CodePudding user response：

I fixed my issue by adding this->mapLayerCollision.emplace_back(); to every while loop. Revised code:

void someFunc {
    std::stringstream value;
    std::vector<std::vector<int>> mapLayerCollision;
    int row = 0;

    for(int i = 0; i < gid_list.length(); i  ) {
        if(gid_list[i] == ',') {
            value.str("");
            int j = 1;
            while (gid_list[i-j] != ',' and i - j > 0) {
                this->mapLayerCollision.emplace_back();
                j  ;
            }
            j--;
            value.str("");
            std::cout << "j: " << j << std::endl;
            while (j > 0) {
                this->mapLayerCollision.emplace_back();
                value << gid_list[i-j];
                j--;
            }
            mapLayerCollision[row].push_back(std::stoi(value.str()));
            value.str("");
        }
        
        else if(gid_list[i] == '\n') {
            value.str("");
            int j = 1;
            while (gid_list[i-j] != ',') {
                j  ;
            }
            j--;
            value.str("");
            while (j > 0) {
                this->mapLayerCollision.emplace_back();
                value << gid_list[i-j];
                j--;
            }
            value.str("");
            row  ;
        }
    }
}