Question

I have an OpenGL program, but can’t alloc correctly.

m_VertexData = (GLfloat*)malloc(sizeof(m_TempVertexData));
m_NormalData = (GLfloat*)malloc(sizeof(m_TempNormalData));
NSLog(@"sizeOfTempVertex: %d sizeOfTempNormal: %d", sizeof(m_TempVertexData),sizeof(m_TempNormalData));
NSLog(@"sizeOfVertex: %d sizeOfNormal: %d",sizeof(m_VertexData),sizeof(m_NormalData));

NSLog:

sizeOfTempVertex: 432 sizeOfTempNormal: 432

sizeOfVertex: 4 sizeOfNormal: 4

Answer 1

m_VertexData and m_normalData are pointers, so their size is sizeof (whatever type it has *), so it allocates the correct amount of memory. You need to allocate sizeof(member of the array) * number of items bytes of memory. By the way, a few things related to malloc:

1. Don’t cast the return value of malloc. It makes code unreadable and it’s unnecessary as void * is implicitly promoted to whatever pointer type it is assigned to.
2. Don’t use sizeof(type), rather sizeof(variable). If you ever change the type of the variable, it’s gonna cause hard-to-track-down errors.

Considering these points, use the following code:

m_VertexData = malloc(sizeof(*m_VertexData) * numberOfItems);