using enum for an array index in c++ - c++

Question

#include <stdlib.h>
#include <stdio.h>
using namespace std;
void main(){
char *resolutions[] = { "720x480", "1024x600", "1280x720", "1920x1080" };
int x = 0;
enum ResMode
{
p480,
p600,
p720,
p1080
};
ResMode res = p480;
printf("\nPlease enter the resolution you wish to use now by entering a number");
printf("\n480p[0], 600p[1], 720p[2], 1080p[3]");
gets(res);
printf("\nThe resolution you have selected is %s", resolutions[res]);
}
so basically i want to be able to press 1 and have it select p600 from enum and out put it as 1024x600 in the next line. I am getting a type conversion error.
How can i fix this?

Answer 1

Looks like you want to associate some items with other items. Usually associations are described in lookup tables or maps.
std::map<ResMode, std::string> map_table =
{
{p480, string("720x480")},
{p600, string("1024x600")},
{p720, string("1280x720")},
{p1080, string("1920x1080")},
};
int main(void)
{
cout << map_table[p480] << "\n";
return EXIT_SUCCESS;
}
Likewise, you can map menu selections to enums.
Edit 1
std::map<unsigned int, ResMode> selection_map =
{
{0, p480}, {1, p600}, {2, p720}, {3, p1080},
};
int main(void)
{
cout << "\n"
<< "Please enter the resolution you wish to use now by entering a number\n"
<<"480p[0], 600p[1], 720p[2], 1080p[3]";
unsigned int selection = 0;
cin >> selection;
if (selection < 4)
{
Resmode resolution_index = selection_map[selection];
cout << "You chose: "
<< map_table[resolution_index]
<< "\n";
}
return EXIT_SUCCESS;
}

Answer 2

int's are not implicitly convertible to an enum. You will have to read in an int and then cast it yourself. Example,
int resInt;
scanf("%d", &resInt);
res = static_cast<ResMode>(resInt);//Note that this does not do bound checking.

Answer 3

You can use "scanf" instead of "gets", something like this:
scanf("%d",&res); // I recommend use scanf_s
Or the iostream library with std::cin. But after taking the input, always, check if the input is the correct one.

Answer 4

As otehrs pointed out, there is no direct way of doing this. However, there are some recipes/tricks that you can use. I modified your code as follows:
#include <stdlib.h>
#include <stdio.h>
#define SOME_ENUM(DO) \
DO(_720x480) \
DO(_1024x600) \
DO(_1280x720) \
DO(_1920x1080)
#define MAKE_ENUM(VAR) VAR,
enum class RESOLUTIONS
{
SOME_ENUM(MAKE_ENUM)
};
#define MAKE_STRINGS(VAR) #VAR,
const char* const
RESOLUTION_NAMES[] =
{
SOME_ENUM(MAKE_STRINGS)
};
const char *
GET_RESOLUTION_NAME(RESOLUTIONS type)
{
return RESOLUTION_NAMES[static_cast<int>(type)];
}
int
GET_RESOLUTION_VALUE(RESOLUTIONS type)
{
return static_cast<int>(type);
}
RESOLUTIONS
GET_RESOLUTION(int i)
{
return static_cast<RESOLUTIONS>(i);
}
using namespace std;
int main(){
printf("\nPlease enter the resolution you wish to use now by entering a number");
printf("\n480p[0], 600p[1], 720p[2], 1080p[3]");
int res_type;
cin >> res_type;
RESOLUTIONS selected_res = GET_RESOLUTION(res_type);
printf("\nThe resolution you have selected is %s\n\n", GET_RESOLUTION_NAME(selected_res));
return 0;
}
Sorry for not providing an explanation, as I have to go now. This recipe can be found here. The code works and compiles for c++11.