2 backslash cause problem

[yazi1297]

Code like this:

try
{
    std::string strJson = "{\"file_path\":\"C\\123.txt\"}";
    nlohmann::json jsonMsg = nlohmann::json::parse(strJson);
    std::string strJsonDump = jsonMsg.dump();
    std::cout << strJsonDump << std::endl;
}
catch (const std::exception& e)
{
    const char* szErrInfo = e.what();
    printf("%s \n", szErrInfo);
}

It will crash, and error log is

[json.exception.parse_error.101] parse error at line 1, column 17: syntax error while parsing value - invalid string: forbidden character after backslash; last read: '"C\1'

What is the issue you have?

When I analyze json code which have 2 backslash, my proejct will crash.

Please describe the steps to reproduce the issue.

1. Create a console project
2. Include Json.hpp in your project
3. Copy the code above into your main function, and run.

Can you provide a small but working code example?

#include "pch.h"
#include <iostream>
#include <string>
#include "json/json.hpp"
int main()
{
    try
    {
        std::string strJson = "{\"file_path\":\"C:\\123.txt\"}";
        nlohmann::json jsonMsg = nlohmann::json::parse(strJson);
        std::string strJsonDump = jsonMsg.dump();
        std::cout << strJsonDump << std::endl;
    }
    catch (const std::exception& e)
    {
        std::cout << e.what() << std::endl;
    }
    std::cout << "Hello World!\n";
}

What is the expected behavior?

It should print {"file_path":"C:\123.txt"} on the screen

And what is the actual behavior instead?

It crashed.

Which compiler and operating system are you using?

• Compiler: vs2019 + Visual Studio 2017 - Windows XP (v141_xp)
• Operating system: Windows

Which version of the library did you use?

• [] latest release version 3.9.1
• other release - please state the version: ___
• the develop branch
  develop + 3.9.1

If you experience a compilation error: can you compile and run the unit tests?

• yes
• no - please copy/paste the error message below

[nlohmann]

The literal "{\"file_path\":\"C\\123.txt\"}" after escaping is "{"file_path":"C\123.txt"}". In JSON, a 1 is not allowed after a backslash - this is what the exception message is saying.

[gregmarr]

To get your desired result, you need to escape twice, once for JSON and one for std::string.

std::string strJson = "{\"file_path\":\"C:\\\\123.txt\"}";

or you can use a raw string literal and only escape once

std::string strJson = R"({ "file_path": "C:\\123.txt" })";

https://en.cppreference.com/w/cpp/language/string_literal

[nlohmann]

@yazi1297 Do you need further assistance with this issue?

[AronZhi]

use a raw string literal seems not work