char[] or *char malloc?

Question

What difference in C between

char text[10]

or

char *char = (char *)malloc(10*sizeof(char)); 

What advantage of using malloc on a pointer?

Answer 1

The first allocates 10 locations in memory (probably in the stack, but it depends on the context where it’s being used) for a type char that in the case has guaranteed size of 1 byte. And this storage location will be called text.

The second allocates memory in the heap also for 10 positions of type char (sizeof(char) is unnecessary). The function malloc() return a pointer to the location of the allocated memory and this pointer can be stored in the variable (in this case it was called char, but that name is invalid).

The use of malloc() which is stored in the heap allows the object to survive even after the function (or stack frame) end. If it were allocated to stack, he is destroyed at the end of stack frame where it was allocated. It may also be a problem for the stack if the size to allocate is large or not easily determined as small.

If you don’t have one free() somewhere there will probably be a memory leak.

In C++ it is not recommended to use either.

Further reading:

• What are and where are the "stack" and "heap"?
• Data access performance in heap and stack and object allocation
• Dynamic Memory Allocation X vector
• Difference between char array and char pointer
• When Stack Overflow Occurs?
• This prevents an array from being initialized with a variable size in C?

Answer 2

The main advantage is that you don’t need to know the size (in your case, 10) a priori. If you know exactly how much space you need when creating your program, and you will only use that memory address within the function where the variable is declared (see next paragraph), then using the first syntax is more convenient (since you don’t have to worry about releasing the allocated memory).

Like malloc allocates space in heap instead of on the stack, the allocated value can be valid even after the function where it is started ends - on the stack when the function (scope) ends, the stack space is released; on the heap you are responsible for releasing the memory.