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10 Mar. 2020
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#include <stdint.h>
#include <stdio.h>
#include <type_traits> // std::is_same()
// Templates: https://www.tutorialspoint.com/cplusplus/cpp_templates.htm
// Goal: test the inputs to a "C macro" (Templated function in this case in C++) to ensure
// they are 1) all the same type, and 2) an unsigned integer type
// 1. This template forces all input parameters to be of the *exact same type*, even
// though that type isn't fixed to one type! This is because all 4 inputs to test_func()
// are of type `T`.
template <typename T>
void test_func(T a, T b, T c, T d)
{
printf("test_func: a = %u; b = %u; c = %u; d = %u\n", a, b, c, d);
// 2. The 2nd half of the check:
// check to see if the type being passed in is uint8_t OR uint16_t OR uint32_t OR uint64_t!
static_assert(std::is_same<decltype(a), uint8_t>::value ||
std::is_same<decltype(a), uint16_t>::value ||
std::is_same<decltype(a), uint32_t>::value ||
std::is_same<decltype(a), uint64_t>::value,
"This code expects the type to be an unsigned integer type\n"
"only (uint8_t, uint16_t, uint32_t, or uint64_t).");
}
int main()
{
printf("Begin\n");
// // TEST A: This FAILS the static assert since they aren't unsigned
// int i1 = 10;
// test_func(i1, i1, i1, i1);
// // TEST B: This FAILS to find a valid function from the template since
// // they are all of different types
// uint8_t i2 = 11;
// uint8_t i3 = 12;
// uint32_t i4 = 13;
// uint32_t i5 = 14;
// test_func(i2, i3, i4, i5);
// TEST C: this works!
uint16_t i6 = 15;
uint16_t i7 = 16;
uint16_t i8 = 17;
uint16_t i9 = 18;
test_func(i6, i7, i8, i9);
return 0;
}
/*
TEST A OUTPUT:
main.cpp: In instantiation of ‘void test_func(T, T, T, T) [with T = int]’:
<span class="error_line" onclick="ide.gotoLine('main.cpp',46)">main.cpp:46:29</span>: required from here
main.cpp:32:5: error: static assertion failed: This code expects the type to be an unsigned integer type
only (uint8_t, uint16_t, uint32_t, or uint64_t).
static_assert(std::is_same<decltype(a), uint8_t>::value ||
^~~~~~~~~~~~~
TEST B OUTPUT:
main.cpp: In function ‘int main()’:
main.cpp:54:29: error: no matching function for call to ‘test_func(uint8_t&, uint8_t&, uint32_t&, uint32_t&)’
test_func(i2, i3, i4, i5);
^
main.cpp:26:6: note: candidate: template void test_func(T, T, T, T)
void test_func(T a, T b, T c, T d)
^~~~~~~~~
main.cpp:26:6: note: template argument deduction/substitution failed:
main.cpp:54:29: note: deduced conflicting types for parameter ‘T’ (‘unsigned char’ and ‘unsigned int’)
test_func(i2, i3, i4, i5);
^
TEST C OUTPUT:
Begin
test_func: a = 15; b = 16; c = 17; d = 18
*/
