Getting strange characters in fields with output from json c++

Question

I'm using the json value I receive from my .get(movie) function to get the values of each of the keys within my json movie object. I'm trying to output it into fields in a fltk GUI, which need to be const char * type. However, I'm getting strange characters instead of my values. Is there an obvious issue here?

 Json::Value result = m.get(movie);
 std::cout << result << endl;
 const char *released = result.get("Released", "NULL").asCString();
 releasedInput->value(released);
 const char *rated = result.get("Rated", "NULL").asCString();
 ratedInput->value(rated);
 Json::Value actors = result.operator[]("Actors");
 const char *plot = result.get("Plot", "NULL").asCString();
 plotMLIn->value(plot);
 const char *runtime = result.get("Runtime", "NULL").asCString();
 runtimeInput->value(runtime);
 Json::Value genre = result.operator[]("Genre");
 const char *filename = result.get("Filename", "NULL").asCString();
 filenameInput->value(filename);
 const char *title = result.get("Title", "NULL").asCString();
 titleInput->value(title)

I've pasted only the relevant lines within my function. If more clarification is needed, I'm happy to provide it.

Have you tried debugging your code? Tried to step through the code, line by line, in a debugger, while monitoring variables and their values? What strings are wrong? *How* are they wrong? What texts did you expect, and what do you actually get? — Some programmer dude, Sep 26 '17 at 07:45
For #1, when I was using std::string, I got the error message that they had to be type const char * so I changed it. For #2, it's because I'm just learning this and, from the documentation, it looked like that was the thing to do. — Kendra, Sep 26 '17 at 07:45
Oh and why are you calling `operator[]` explicitly as a function? Why not e.g. `result["Actors"]`? — Some programmer dude, Sep 26 '17 at 07:45
I'll change that Like I said, I'm new so I must have misinterpreted the documentation for Json::Value. I'm taking in an array there. — Kendra, Sep 26 '17 at 07:49

score 1 · Accepted Answer · answered Sep 26 '17 at 08:19

You should save the result in a std::string and then call c_str() on that string to get a C-string. If you chain those calls and save the pointer instantly or only do asCString() the string object holding the memory the C-string is pointing at will have been cleared and you will invoke undefined behavior in your code which is not what you want.

I.E

std::string runtime = result.get("Runtime", "NULL").asString();
runtimeInput->value(runtime.c_str());

score 0 · Answer 2 · answered Sep 26 '17 at 08:14

0

I got it. I just need to change .asCString(); to asString().c_str();

I'm sure there's a more eloquent way of doing this but, as I said, I'm a newbie.

answered Sep 26 '17 at 08:14

Kendra

125
2
12

This will only appear to work, it's still undefined behavior. – Hatted Rooster Sep 26 '17 at 08:29

Getting strange characters in fields with output from json c++

2 Answers2