why simple Vulkan fails at vkCreateInstance()? - c

Question

I'm trying to vulkanize my life. so I can use Vulkan compute. But creating a simple instance fails every way I tried.
Here is the code :
#include <vulkan/vulkan.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char * argv[])
{
VkApplicationInfo vkAppInfo;
vkAppInfo.sType = VK_STRUCTURE_TYPE_APPLICATION_INFO;
vkAppInfo.apiVersion = VK_API_VERSION_1_0;
VkInstanceCreateInfo vkCreateInfo;
vkCreateInfo.sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO;
vkCreateInfo.pApplicationInfo = &vkAppInfo;
VkInstance instance = VK_NULL_HANDLE;
VkResult result = vkCreateInstance(&vkCreateInfo, NULL, &instance);
return -1;
if (result != VK_SUCCESS) {
return -2;
} else {
return -3;
}
return 0;
}
I tried Vulkan Tutorial (without the graphics function GLFW)

Answer 1

The problem here is that you assume the rest of the fields you do not fill out will be filled out somehow automatically with some valid data, but that is not the case. It will be filled with garbage. Don't forget this is a very general thing in C and C++: Every memory that is not explicitely initialized is just garbage.
I propose you write some wrapper functions for filling your Vulkan structs such as VkApplicationInfo. It could look like this:
VkApplicationInfo fill_app_info(const char* app_name, const char* app_version,
const char* engine_name, uint32_t engine_version,
uint32_t vk_api_version) {
VkApplicationInfo info;
info.sType = VK_STRUCTURE_TYPE_APPLICATION_INFO;
info.pNext = NULL;
info.pApplicationName = app_name;
info.applicationVersion = app_version;
info.pEngineName = engine_name;
info.engineVersion = engine_version;
info.apiVersion = vk_api_version;
return info;
}
This might seem not worth it for VkApplicationInfo, but there are Vulkan structures you will need more often.
Once you wrote the most verbose version of fill_app_info, you can use two powerful tools to make it even more easy for you: default parameters and overloading:
// This is even better: it has default parameters
VkApplicationInfo fill_app_info(const char* app_name, const char* app_version,
const char* engine_name = "MyEngine",
uint32_t engine_version = VK_MAKE_VERSION(1,0,0),
uint32_t vk_api_version = VK_API_VERSION_1_2) {
VkApplicationInfo info;
info.sType = VK_STRUCTURE_TYPE_APPLICATION_INFO;
info.pNext = NULL;
info.pApplicationName = app_name;
info.applicationVersion = app_version;
info.pEngineName = engine_name;
info.engineVersion = engine_version;
info.apiVersion = vk_api_version;
return info;
}
VkApplicationInfo fill_app_info(const char* app_name) {
// Call the other function
return fill_app_info(app_name, VK_MAKE_VERSION(1,0,0));
}
// Call function 1 with all parameters specified
VkApplicationInfo example1 = fill_app_info("MyApp", VK_MAKE_VERSION(1,0,0),
"MyCustomEngine1000", VK_MAKE_VERSION(1,0,6),
VK_API_VERSION_1_1);
// Call function 1 and use default parameters
VkApplicationInfo example2 = fill_app_info("MyApp", VK_MAKE_VERSION(1,0,0));
// Call function 2 and let it fill out everything but the app name
VkApplicationInfo example3 = fill_app_info("MyApp");
As you can see, example3 is created with only one argument specified. This makes your overall code much shorter if you create functions like this for all Vulkan structs. In Vulkan we often have the that we do need to fill out all members of the struct, even if some of the members are not really used. I would also suggest to enable validation layers to check if you use the API ccorrectly. Also, read the Vulkan docs. They tell you how to fill out every struct correctly: https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkApplicationInfo.html