Corrupted characters in std::string

munderwoods

Hey, I've been researching this issue for a bit not and I just can't resolve it. I'm passing strings into a function and sticking it in a new thread, but when the strings get to the new function the first few characters are almost always corrupted. I'm on ubuntu running qt 5 with g++, and c++ 11. I tried adding CONFIG += c++11 to my .pro file, but same problem. Here is the code:

How the function is called:

std::string idToken = firebaseTokens.at("idToken");
std::thread thread(startStream, std::ref(databaseURL), std::ref(locationId), std::ref(idToken));

How it is defined:

static void startStream(std::string databaseURL, std::string locationId, std::string idToken)
{
  std::string fullUrl = std::string(databaseURL + locationId + ".json" + "?" + paramsString(
    {{"auth", idToken}}
  ));

  std::string response = httpRequest(fullUrl, "GET", "", "", true);
}

When I cout idToken outside of the function call it starts like:

eyJhbGciOiJSUzI1NiIsImtpZCI6IjU4ODI0YTI2ZjFlY2Q1NjEyN2U4OWY1YzkwYTg4MDYxMTJhYmU5OWMiLCJ0eXAiOiJKV1QifQ

Inside of the function call it starts like:

hUrUNiIsImtpZCI6IjU4ODI0YTI2ZjFlY2Q1NjEyN2U4OWY1YzkwYTg4MDYxMTJhYmU5OWMiLCJ0eXAiOiJKV1QifQ

You can see here that only the first few characters are wrong, and the end string is always a bit shorter.

Any info on how to proceed would be greatly appreciated, thanks.

ChrisW67

Nothing to do with Qt. This code is all standard C++ that works fine here (with or without std::ref()):

#include <iostream>
#include <string>
#include <thread>
#include <chrono>

static void startStream(std::string databaseURL, std::string locationId, std::string idToken)
{
        std::this_thread::sleep_for(std::chrono::seconds(5));
        std::cout << "startStream()" << std::endl;
        std::cout << databaseURL << std::endl;
        std::cout << locationId << std::endl;
        std::cout << idToken << std::endl;
}


int main()
{
        std::string databaseURL("http://dummy.local/url");
        std::string locationId("dummyLocationId");
        std::string idToken("eyJhbGciOiJSUzI1NiIsImtpZCI6IjU4ODI0YTI2ZjFlY2Q1NjEyN2U4OWY1YzkwYTg4MDYxMTJhYmU5OWMiLCJ0eXAiOiJKV1QifQ");

        std::cout << "main()" << std::endl;
        std::cout << databaseURL << std::endl;
        std::cout << locationId << std::endl;
        std::cout << idToken << std::endl;
        std::thread thread(startStream, std::ref(databaseURL), std::ref(locationId), std::ref(idToken));

        thread.join();
        return 0;
}

$ g++ -o test main.cpp  && ./test
main()
http://dummy.local/url
dummyLocationId
eyJhbGciOiJSUzI1NiIsImtpZCI6IjU4ODI0YTI2ZjFlY2Q1NjEyN2U4OWY1YzkwYTg4MDYxMTJhYmU5OWMiLCJ0eXAiOiJKV1QifQ
startStream()
http://dummy.local/url
dummyLocationId
eyJhbGciOiJSUzI1NiIsImtpZCI6IjU4ODI0YTI2ZjFlY2Q1NjEyN2U4OWY1YzkwYTg4MDYxMTJhYmU5OWMiLCJ0eXAiOiJKV1QifQ

Something else about your code is at issue. Start by ensuring a consistent, clean build.

munderwoods

@ChrisW67 Welp, thanks. I'm pretty new to c++, so I don't really know where to start with something like this, but I'll backtrack and go at it all again.

You're sure it's not related to this, though? https://stackoverflow.com/questions/38622444/stdstring-values-become-corrupted-in-qt-5
I did try the fix and that didn't help so that's a point against it of course.

The problem only cropped up when I added qt to the project though.

ChrisW67

@munderwoods Simply referring to the Qt5 libraries should not do anything. Passing the strings through a Qt function might. Can you produce a small program like mine that fails?

munderwoods

@ChrisW67 Nope, I can not. I'll rebuild from the ground up. Thanks.

munderwoods

@munderwoods Looks like it only happens when I detach the thread, it actually works consistently if I join it...

Christian Ehrlicher

@munderwoods said in Corrupted characters in std::string:

Looks like it only happens when I detach the thread, it actually works consistently if I join it...

Correct, because idToken is already destructed when the thread runs because you only pass a reference to the thread and idToken is a local variable. At least this is what it looks like from your code pieces. Please provide a minimal, compilable example.

munderwoods

@Christian-Ehrlicher You were right, I was declaring my variables locally then they were being destroyed as soon as I detached the thread. It was webdev thinking. Sorry to waste everyone's time!