how to get error line number in C++ program

Question

I want to handle errors in my c++ program, so I created some exception classes to manage those errors, but I want to specify at which line in my program the error occurred.

I passed LINE macro to the constructor of my exception class.

For example:

void f(int i){ // LINE A
  if(i<0)
    throw(OutOfRange("message", __LINE__); // LINE B
}

void main(){

  try{
    f(-6); // LINE C
  }
  catch(const OutOfRange& error){
    //do something
  }

}

In this example I can only get the LINE B number, but I want to get LINE A and LINE C numbers.

Any idea, where and how to use LINE macro ??

Thanks.

Answer 1

You are looking for a stack trace and there's no portable way to get it. Something somewhat similar can be achieved with:

struct SourcePoint
{
    const char *filename;
    int line;
    SourcePoint(const char *filename, int line)
      : filename(filename), line(line)
    { }
};

std::vector<SourcePoint> callstack;

struct SourcePointMarker
{
    SourcePointMarker(const char *filename, int line)
    {
        callstack.push_back(SourcePoint(filename, line);
    }

    ~SourcePointMarker()
    {
        callstack.pop_back();
    }
}

#define MARK_FUNCTION \
  SourcePointMarker sourcepointmarker(__FILE__, __LINE__);

Then right after the beginning of each function (or point of interest) you just add a line... for example

int myFunction(int x)
{
    MARK_FUNCTION
    ...
}

Using this approach in your error handlers you can know who was called by who and so on (of course you will know only functions or places that have been instrumented with MARK_FUNCTION). If this is needed only during testing (and not in production) then probably you should just enable core dumps and learn how to run a debugger in post-mortem analysis.

Answer 2

You need a stack trace and a debugger. There's no way in Standard C++ that you could find line C without passing it in as an argument (f(-6, __LINE__)), and no way at all that you could find Line A.