为什么从方法获取vulkan扩展会使vulkan实例创建失败？

Question

I am following the vulkan-tutorial.com tutorial and im on the validation layers step. In the tutorial Alexander Overvoorde the author moved the gathering of available extensions for instance creation to its own function.

std::vector<const char*> getRequiredExtensions()

Previously i had gathered that info a little differently because i am using SDL2 instead of glfw, but my program ran with instance creation and no validation errors. Problem is when i moved the code to this function i can no longer get instance creation.

this worked fine:

unsigned int extensionCount = 0;
vkEnumerateInstanceExtensionProperties(NULL, &extensionCount, NULL);
std::vector<VkExtensionProperties> extensionProperties(extensionCount);
vkEnumerateInstanceExtensionProperties(NULL, &extensionCount, extensionProperties.data());
std::vector<const char*> extensionNames;
std::cout << "available extensions:" << std::endl;
int i = 0;
while (i < extensionCount) {
    extensionNames.push_back(extensionProperties[i].extensionName);
    std::cout << extensionNames[i] << std::endl;
    i++;
}
if (enableValidationLayers) {
    extensionNames.push_back(VK_EXT_DEBUG_REPORT_EXTENSION_NAME);
}*/
createInfo.enabledExtensionCount = extensionCount;
createInfo.ppEnabledExtensionNames = extensionNames.data();

but this failed even though the function uses the exact same code and returns extensionNames, i then use it like this:

std::vector<const char*> extensionNames = getRequiredExtensions();
createInfo.enabledExtensionCount = static_cast<uint32_t>(extensionNames.size());
createInfo.ppEnabledExtensionNames = extensionNames.data();

So why doesn't this work? I have a formally taught background of java but have coded in c++ for a year, so it is possibly like a syntax error or pointer that i am sending wrong. Additionally

reateInfo.enabledExtensionCount = static_cast<uint32_t>(getRequiredExtensions().size());

works just fine so the returned vector is of the correct size: 5 i believe because i have 4 extensions plus the debug one.

Answer 1

From the documentation at Khronos.org , VkExtensionProperties looks like this:

typedef struct VkExtensionProperties {
    char        extensionName[VK_MAX_EXTENSION_NAME_SIZE];
    uint32_t    specVersion;
} VkExtensionProperties;

... so on this line:

extensionNames.push_back(extensionProperties[i].extensionName);

... what you're storing into extensionNames are pointers to arrays that live in extensionProperties , which is local to your function. When you return from the function, all of the arrays are destructed along with extensionProperties , and all of your pointers are now dangling.
What you get then is undefined behaviour when Vulkan tries to use these dead pointers.