std::remove_if and std::isspace - compile-time error - c++

Question

I have the following code:
#include <algorithm>
#include <cctype>
#include <string>
int main()
{
std::string str;
str.erase(std::remove_if(str.begin(), str.end(), std::isspace), str.end());
}
MSVC-11.0 compiles this code without any error, but gcc 4.7.2 gives me the following errors:
main.cpp: In function ‘int main()’:
main.cpp:8:66: error: no matching function for call to ‘remove_if(std::basic_string<char>::iterator, std::basic_string<char>::iterator, <unresolved overloaded function type>)’
main.cpp:8:66: note: candidate is:
In file included from /usr/include/c++/4.7/algorithm:63:0,
from main.cpp:1:
/usr/include/c++/4.7/bits/stl_algo.h:1160:5: note: template<class _FIter, class _Predicate> _FIter std::remove_if(_FIter, _FIter, _Predicate)
/usr/include/c++/4.7/bits/stl_algo.h:1160:5: note: template argument deduction/substitution failed:
main.cpp:8:66: note: couldn't deduce template parameter ‘_Predicate’
I found this question about it, but according to the cppreference, there isn't any version of this function that takes two arguments. I found this question too, but according to the cppreference (yep, again) I see that there's only one std::isspace function overload.
Who's right? What am I doing wrong? How can I fix it?

Answer 1

There is another overload of std::isspace, so you need to specify which one to use. An easy way is to use a lambda (or write your own one-line function if you don't have C++11 support):
std::remove_if(str.begin(), str.end(),
[](char c){
return std::isspace(static_cast<unsigned char>(c));
});

Answer 2

std::isspace is an overloaded function, although the two overloads reside in different headers. Also note that your code may introduce undefined behaviour because only values in the range 0..UCHAR_MAX can be passed to std::isspace, whereas a char is possibly signed.
Here is a solution:
std::string str;
auto f = [](unsigned char const c) { return std::isspace(c); };
str.erase(std::remove_if(str.begin(), str.end(), f), str.end());

Answer 3

The following solution should get you around the compile-time error:
str.erase(std::remove_if(str.begin(), str.end(), (int(*) (int)) std::isspace), str.end());

Answer 4

After C++ 11, you can use lamda function (easier to understand), see below:
string s = " 3/ 2";
auto isSpace = [](const unsigned char c)
{
return std::isspace(c);
};
s.erase(remove_if(s.begin(), s.end(), isSpace), s.end());
Output:
3/2