Use of for_each on map elements

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北荒 2021-01-30 10:29

I have a map where I\'d like to perform a call on every data type object member function. I yet know how to do this on any sequence but, is it possible to do it on an associativ

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不思量自难忘° (楼主)

2021-01-30 11:09
It's unfortunate that you don't have Boost however if your STL implementation has the extensions then you can compose mem_fun_ref and select2nd to create a single functor suitable for use with for_each. The code would look something like this:
```
#include 
#include 
#include    // GNU-specific extension for functor classes missing from standard STL

using namespace __gnu_cxx;  // for compose1 and select2nd

class MyClass
{
public:
    void Method() const;
};

std::map Map;

int main(void)
{
    std::for_each(Map.begin(), Map.end(), compose1(std::mem_fun_ref(&MyClass::Method), select2nd::value_type>()));
}
```
Note that if you don't have access to compose1 (or the unary_compose template) and select2nd, they are fairly easy to write.
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