How to detect data types from string?

Question

There is a pseudocode:

s = input()

if s == 'int':
    func<int>(...)
if s == 'char':
    func<char>(...)
and there're more if blocks

How can I write code that can do this without any if. Like code below:

s = input()
func<s>(...) #auto detect type in s

I need a solution in C++.

Answer 1

Although this is not directly possible with templated functions, I recommend a table lookup of std::string vs. function pointer.

For example:

typedef void (*Function_Pointer_Type)(void);  
struct Table_Entry
{
  char const * data_type_name;
  Function_Pointer_Type data_type_function;
};

void Process_Int(void);
void Process_Double(void);

static const Table_Entry data_type_function_table[] =
{
  {"int", Process_Int},
  {"double", Process_Double},
};
static const unsigned int number_of_data_types =
  sizeof(data_type_function_table) / sizeof(data_type_function_table[0]);

// ...
for (unsigned int i = 0; i < number_of_data_types; ++i)
{
  if (s == data_type_function_table[i].data_type_name)
  {
    data_type_function_table.data_type_function();
    break;
  }
}

Another method is to use std::map<std::string, Function_Pointer_Type>. The map must be initialized before it is used. The static, constant table doesn't need to be initialized at runtime.