A nice comparison on converting a string to int:

C++ String to Int

by Ivan Neeson

From the article:

In this post I will compare the following methods for parsing a string into an integer in C++:

• Manually
• atoi()
• strtol()
• sscanf()
• std::stoi (C++11 only)
• std::istringstream
• Boost.LexicalCast
• Boost.LexicalCast with C locale
• Boost.Spirit.Qi
• Boost.Coerce

But first lets look at the requirements...