Convert C++ string variable to long

Question

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*)'

Answer 1

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

Answer 2

试试这样：

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

Answer 3

使用std :: stol <字符填充空格>

Answer 4

Use a string stream.

#include <sstream>

// code...
std::string text;
std::stringstream buffer(text);
long var;
buffer >> var;

Answer 5

如果您无法访问C ++ 11，并且可以使用boost库，则可以考虑以下选项：

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