Print to locate the error code block - c++

Question

Hi great C++ programmers,
I've been in this situation many times, but I still don't know how to solve it.
I am programming in C++ in Rstudio, and my program runs into a fatal error which needs me to restart. I want to locate where the mistake is in my code. What I often do is adding some detection lines like:
int main()
{
...code block;
std::cout<<"1.1\n";
...code block;
std::cout<<"1.2\n";
...code block;
std::cout<<"1.3\n";
...code block;
std::cout<<"1.4\n";
return 1;
}
Then I run the code.
The weird thing is, before it runs into "fatal error", sometimes I got "1.1" printed on the console, sometimes I got "1.1" and "1.2", sometimes I got "1.1", "1.2" and "1.3, and sometimes I got nothing.
I guess it has something to do with the operating system because it is the operating system that got the order to print something which would take some time, but meanwhile the CPU was executing forward the code and met the fatal error.
Or, maybe it's the way the codes were compiled that results in such thing?
Is there anyway to solve it? I just want the program to print out everything I asked before it runs into "fatal error".
Thanks!
The compiler optimization could reorder the code, making the printouts unreliable. You are coding C++ in the R environment, and the default g++ compiler optimization is set to -O2. Go to your R directory, search for a file named "Makeconf". Open it with a text editor, locate command "CXX11FLAGS = -O2 ...", erase "-O2", save the file and rebuild your program. Other commands like "CXXFLAGS = -O2 ..." may also need to be modified. Code will run in strictly sequential order by then.

Answer 1

You are using std::cout which is not what R uses, and you get caught up in two different buffering schemes.
Easy solution: use Rcpp::Rcout instead which redirects into R's output stream.