write temporary variable to Json : I get \u0000

Question

I am facing a strange problem : when i try to add a Json variable inside a for loop, it is not written properly in the output file whereas it works well outside the loop (rapidJson v0.11).

Edit : the loop is not the problem but the bug appears even only with brackets

Here is a sample of my code :

rapidjson::Document output;
output.SetObject();
rapidjson::Document::AllocatorType& allocator = output.GetAllocator();

{
    std::string s1("test");
    output.AddMember("test_field",s1.c_str(), allocator);
}
std::string s2("test");
output.AddMember("test_field2",s2.c_str(), allocator);

rapidjson::FileStream f(stdout);
rapidjson::PrettyWriter<rapidjson::FileStream> writer(f);
output.Accept(writer);

The output I get is :

{"test_field": "\u0000est", 
"test_field2": "test"}

So there seems to be a problem with the variable added inside the bracket.. Do you have any idea where it comes from ?

Answer 1

Thanks to Steve I managed to find the answer :

as said in the documentation : "rapidjson provide two strategies for storing string.

1. copy-string: allocates a buffer, and then copy the source data into it.
2. const-string: simply store a pointer of string. "

So the right way to do what I wanted is :

rapidjson::Document output;
output.SetObject();
rapidjson::Document::AllocatorType& allocator = output.GetAllocator();

{
    std::string s1("test");
    rapidjson::Value field;
    char buffer[10];
    int len = sprintf(buffer, s1); .
    field.SetString(buffer, len, allocator);

    output.AddMember("test_field",field, allocator);
}
std::string s2("test");
output.AddMember("test_field2",s2.c_str(), allocator);

rapidjson::FileStream f(stdout);
rapidjson::PrettyWriter<rapidjson::FileStream> writer(f);
output.Accept(writer);

The output I get is now :

 {"test_field": "test", 
  "test_field2": "test"}