std::map not storing any values

Question

I have the following code:

DataHandler::DataHandler(){
    //just call the constructor with the default file.
    DataHandler(DEFAULT_FILE);
}

DataHandler::DataHandler(const char* filename){
    RefreshFromFile(filename);
}

void DataHandler::Refresh(){
    RefreshFromFile(DEFAULT_FILE);
}

void DataHandler::RefreshFromFile(const char* filename){
    std::string line, key, value;
    std::ifstream file(filename);
    if(file.is_open()){
        while(std::getline(file, line)){
            key = Base64Decode(line.substr(0, line.find(" ")));
            value = Base64Decode(line.substr(line.find(" ")+1));
            float floatValue = atof(value.c_str());
            values[std::string(key)] = floatValue;
            std::cout << "values[\"" << key << "\"] = " << values[key] << std::endl;
        }
    }
    file.close();
}

float DataHandler::operator[](std::string index){
    if(values.find(index) == values.end()){
        fprintf(stderr, "ERROR: Value %s not found, returning 0.0 \n", index.c_str());
        return 0.0f;
    }else{
        return values[index];
    }
}

This all works neatly, and I get the following debug messages:

values["DRIVE_SPEED"] = 1
values["GRAB_WHEEL_SPEED"] = 0.2
values["GRAB_WHEEL_TURBO_SPEED"] = 0.6

If I try to get the size of the map, it returns 3.

But when I try to index anything, I get a not found message.

#include "DataHandler.hpp"
#include <iostream>

int main(int argc, const char * argv[])
{
    DataHandler data;
    data.Debug();
    std::cout << data["DRIVE_SPEED"] << std::endl;
    return 0;
}

What is wrong with my code?

Answer 1

DataHandler::DataHandler(){
    //just call the constructor with the default file.
    DataHandler(DEFAULT_FILE);
}

This code doesn't do what you think it does. It doesn't delegate the constructor call (as it would in Java, IIRR). Instead, it creates a temporary DataHandler initialised with DEFAULT_FILE, which is immediately destroyed again. The "correct" debug output you see comes from this temporary.

To solve this, drop the default constructor and change the single-parameter one like this:

DataHandler::DataHandler(const char* filename = DEFAULT_FILE) {
    RefreshFromFile(filename);
}