Simple string parsing with C++

Question

I\'ve been using C++ for quite a long time now but nevertheless I tend to fall back on scanf when I have to parse simple text files. For example given a config

Answer 1

Boost.Spirit is not reserved to parse complicated structure. It is quite good at micro-parsing too, and almost match the compactness of the C + scanf snippet :

#include 
#include 
#include 

using namespace boost::spirit::qi;


int main()
{
   std::string text = "foo: [3 4 5]\nbaz: 3.0";
   std::istringstream iss(text);

   std::string line;
   while (std::getline(iss, line))
   {
      int x, y, z;
      if(phrase_parse(line.begin(), line.end(), "foo: [">> int_ >> int_ >> int_ >> "]", space, x, y, z))
         continue;
      float w;
      if(phrase_parse(line.begin(), line.end(), "baz: ">> float_, space , w))
         continue;
   }
}

(Why they didn't add a "container" version is beyond me, it would be much more convenient if we could just write :

if(phrase_parse(line, "foo: [">> int_ >> int_ >> int_ >> "]", space, x, y, z))
   continue;

But it's true that :

• It adds a lot of compile time overhead.
• Error messages are brutal. If you make a small mistake with scanf, you just run your program and immediately get a segfault or an absurd parsed value. Make a small mistake with spirit and you will get hopeless gigantic error messages from the compiler and it takes a LOT of practice with boost.spirit to understand them.

So ultimately, for simple parsing I use scanf like everyone else...