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 );

来源：https://stackoverflow.com/questions/11776210/convert-c-string-variable-to-long