str::find() function for the const char* - c++

Question

const char *attribute[] =
{"abc","efg","hij","lmn","opq","rst","uvw","Xyz"};
want to find Boolean and location of the "lmn" in the above array.

Answer 1

This example will show you how to get both a bool and an index back.
Demo here : https://onlinegdb.com/vHHJ9QG1M
#include <array>
#include <limits>
#include <algorithm>
#include <iostream>
#include <string_view>
// make a struct to be able to return two (readable) values from function
// I almost never use std::pair it results in hard to read code.
// where you have to check the semantics of first/second over and over again.
struct is_attribute_result_t
{
// conversion to bool so result can be directly used in "if's"
constexpr operator bool() const
{
return is_attribute;
}
bool is_attribute{false};
std::size_t index{std::numeric_limits<std::size_t>::max()};
};
// make a std::array that is usable at compile time
// use string_view because it implements operator== for the whole string (const char* doesn't)
constexpr std::array<std::string_view,8> attributes = {"abc","efg","hij","lmn","opq","rst","uvw","xyz"};
// make a function that can be evaluated at compile time
// so no std::find, just use availability of (constexpr) operator== on string_view
constexpr is_attribute_result_t test_attribute(const std::string_view& attribute)
{
is_attribute_result_t result;
for(std::size_t n = 0; n < attributes.size(); ++n)
{
if(attribute == attributes[n])
{
result.is_attribute = true;
result.index = n;
return result;
}
}
return result;
}
int main()
{
// nice thing is you can now also check at compile time.
static_assert(test_attribute("abc"));
static_assert(test_attribute("abc").index == 0ul);
static_assert(test_attribute("lmn"));
static_assert(test_attribute("lmn").index == 3ul);
static_assert(!test_attribute("123"));
// and ofcourse still use the function at runtime too
if ( auto result = test_attribute("lmn"))
{
std::cout << "lmn is an attribute, and is found at index = " << result.index << "\n";
}
return 0;
}