Can I cast an unsigned char* to an unsigned int*?

c++ memory-management static-cast
David Mulder picture David Mulder · Mar 31, 2014 · Viewed 7.5k times · Source 
error: invalid static_cast from type ‘unsigned char*’ to type ‘uint32_t* {aka unsigned int*}’
     uint32_t *starti = static_cast<uint32_t*>(&memory[164]);

I've allocated an array of chars, and I want to read 4 bytes as a 32bit int, but I get a compiler error. I know that I can bit shift, like this:

(start[0] << 24) + (start[1] << 16) + (start[2] << 8) + start[3];

And it will do the same thing, but this is a lot of extra work.

Is it possible to just cast those four bytes as an int somehow?

Answer

user2033018 picture user2033018 · Mar 31, 2014

static_cast is meant to be used for "well-behaved" casts, such as double -> int. You must use reinterpret_cast:

uint32_t *starti = reinterpret_cast<uint32_t*>(&memory[164]);

Or, if you are up to it, C-style casts:

uint32_t *starti = (uint32_t*)&memory[164];

Related questions

In what cases do I use malloc and/or new?

I see in C++ there are multiple ways to allocate and free data and I understand that when you call malloc you should call free and when you use the new operator you should pair with delete and it is …

Read More
Does delete on a pointer to a subclass call the base class destructor?

I have an class A which uses a heap memory allocation for one of its fields. Class A is instantiated and stored as a pointer field in another class (class B. When I'm done with an object of class B, …

Read More
Can a local variable's memory be accessed outside its scope?

I have the following code. #include <iostream> int * foo() { int a = 5; return &a; } int main() { int* p = foo(); std::cout << *p; *p = 8; std::cout << *p; } And the code is just running with no …

Read More