CODEWITHSUNDEEP
c++templates
user1100264
user1100264

Reputation:

Deducing the base type from a template parameter

Visual Studio 2017, C++ with C++17

Is there any way to use a template parameter and deduce the base type?

Example: If the template parameter is std::string I want to declare a char inside the function. If the template parameter is std::basic_string<unsigned char> I want to declare an unsigned char inside the function:

#include <string>
#include <vector>
#include <typeinfo>

using namespace std;

typedef unsigned char uchar;
typedef basic_string<uchar> ustring;

template <typename str>
void exampleFunc(vector<str> &vec)
{
    // Pseudo-code to be evaluated at ***compile time***
    if (typeof(str) == ustring)
        uchar c;
    if (typeof(str) == string)
        char c;

    // ... code ...
}
int main()
{
    vector<string> vec;
    vector<ustring> uvec;

    exampleFunc(vec);
    exampleFunc(uvec);
}

Upvotes: 1

Views: 92

Answers (2)

n. m. could be an AI
n. m. could be an AI

Reputation: 119847

If you only want std::basic_string parameterised by different character types, say so:

template <typename Chr>
void exampleFunc(std::vector<std::basic_string<Chr>> &vec) ...

Upvotes: 7

vahancho
vahancho

Reputation: 21220

What if you write it like:

template <typename str>
void exampleFunc(std::vector<str> &vec)
{
  if constexpr (std::is_base_of<str, std::string>::value)
  {
    char c;
    // ...
  }
  else
  {
    // ...
  }
  // ... code ...
}

Upvotes: 0

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