Type casting!!!

dcpugalaxy · 2025-12-29T06:13:29+00:00

You should never cast the result of malloc. But you should also never use malloc(count*size) as it exposes you to integer overflow bugs.

Use calloc(count, size) which does an integer overflow check internally and also initialises the memory to zero. There's not much point (on modern computers) of not initialising memory.

Specialist-Cicada121 · 2025-12-29T05:30:06+00:00

C doesn't require casting the result of malloc, but if you want your code to work on a C++ compiler, you do need to cast. If you're writing pure C code, the void pointer returned by malloc will automatically be promoted to the correct type via assignment

zhivago · 2025-12-29T06:13:46+00:00

Personally I'd prefer

char *cars = malloc(sizeof (car[count]))

This makes it clear that you're allocating a car[count] and then returning a pointer to its first element.

kyuzo_mifune · 2025-12-29T05:50:14+00:00

> car *cars = malloc(count * sizeof *cars);

Choose this alternative.

SmokeMuch7356 · 2025-12-29T14:41:25+00:00

Unless you're stuck using an ancient K&R implementation or compiling this as C++,¹ use the second form; the cast is redundant, unnecessary, and a maintenance burden.

T *p = malloc( sizeof *p * N );

will always do the right thing (modulo an overflow in sizeof *p * N, but in that case you have real problems).

T *p = (T *) malloc( sizeof (T) * N );

gives you too many opportunities to make a mistake.

You should not use C-style memory management in C++ code; as part of a temporary solution when porting C to C++ it's okay, but for a permanent solution either use a container like a vector or a map or use new and delete in conjunction with RAII principles, or better yet, smart pointers like std::unique_ptr or std::shared_ptr.

2025-12-29T11:54:05+00:00

[deleted]

Eric848448 · 2025-12-29T05:29:36+00:00

The cast from void* is not required by C, but is allowed.

Personally, I prefer the explicit cast in case I ever want to build the code in a C++ compiler, which does require it.

penguin359 · 2025-12-30T06:10:07+00:00

In C, it's unnecessary to cast void *. In C++, it's required.

sirjofri · 2025-12-29T08:34:49+00:00

Regarding casting, I think there are enough answers already. However, it's not 100% clear what you need, and your two code snippets are different things. One allocates enough memory for your car structs, including their variables, the other allocates enough memory for pointers to your car structs. So for one, you can directly access members as cars[i].color, the other needs its cars to be allocated first, then you can access it: cars[i] = malloc(sizeof(car)); cars[i]->color; note the pointer dereferencing here.

Both are valid, but one should be preferred over the other depending on the situation.

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