Trying to get rid of any heap memory allocation

Question

I know how to do it with heap memory, but I try to get rid of any heap memory allocation in my code.

I cannot use any library which can help me, it means: <string> for example.

How can I do it with using stack memory allocation?

int main(void) {
    class Animal {
        unsigned char nameLength;
        unsigned char name[];

        setName(unsigned char name[]) {
            memcpy(this->name, name, this->length * sizeof(unsigned char));
        }
    }

    Animal dog;

    // The value '4' isn't constant, it depends on received data from socket
    dog.nameLength = 4;

    // Right now I know how many elements will be in dog.name array

    unsigned char randomName[dog.nameLength];

    // Here will be a for loop, but just for example:
    randomName[0] = "B";
    randomName[1] = "e";
    randomName[2] = "n";
    randomName[3] = "/0";

    dog.setName(randomName);

    // Expected output: dog.name = "Ben\0"
}

The for loop will look like:

unsigned char i;
for (i = 0; i < (dog.nameLength-1); i++) {
    randomName[i] = packet[i];
}
randomName[i] = 0;

The [mcve] you show have multiple problems, all unrelated to the problem you ask about. — Some programmer dude, Feb 15 '20 at 16:08
And the only way to solve the problem you ask about is to define `Animal::name` with a fixed length, large enough to hold all possible strings you might need. — Some programmer dude, Feb 15 '20 at 16:08
Lastly, *why* can't you use any heap allocation? Is it an assignment requirement? What *is* your assignment? What are its requirements? And please take some time to read [ask], as well as [this question checklist](https://codeblog.jonskeet.uk/2012/11/24/stack-overflow-question-checklist/). — Some programmer dude, Feb 15 '20 at 16:10
`unsigned char randomName[dog.nameLength];` this is not valid C++ because of VLA — Aykhan Hagverdili, Feb 15 '20 at 16:22

score 0 · Answer 1 · answered Feb 15 '20 at 17:07

Your code has multiple issues, please break it down into multiple questions for each problem you are having.

But for the main issue: in general it is a very bad idea to do what you are trying to do (allocate dynamically on the stack), this is exactly what heap allocations are for.

Also, standard C++ does not allow this. There are, however, compiler extensions you could use: Why no variable size array in stack? and linux has alloca: http://man7.org/linux/man-pages/man3/alloca.3.html & C++ How to allocate memory dynamically on stack?

But, again, do not do this unless you really need to and you understand what you are doing.

Also, please listen to the commenters about how to ask a question and provide a minimal example.

Trying to get rid of any heap memory allocation

1 Answers1