Convert C++ string variable to long

问题:

I have a variable:

string item; 

It gets initialized at run-time. I need to convert it to long. How to do it? I have tried atol() and strtol() but I always get following error for strtol() and atol() respectively:

cannot convert 'std::string' to 'const char*' for argument '1' to 'long int strtol(const char*, char**, int)'  cannot convert 'std::string' to 'const char*' for argument '1' to 'long int atol(const char*)' 

回答1:

Try like this:

long i = atol(item.c_str()); 

回答2:

c++11:

long l = std::stol(item); 

http://en.cppreference.com/w/cpp/string/basic_string/stol

C++98:

char * pEnd;. long l = std::strtol(item.c_str(),&pEnd,10); 

http://en.cppreference.com/w/cpp/string/byte/strtol

回答3:

Use std::stol < characters to fill space >

回答4:

Use a string stream.

#include <sstream>  // code... std::string text; std::stringstream buffer(text); long var; buffer >> var; 

回答5:

If you don't have access to C++11, and you can use the boost library, you can consider this option:

long l = boost::lexical_cast< long >( item ); 

文章来源: Convert C++ string variable to long