Some problem in package function（Wrapper function ）in C .How do i package a founction and let the callee founction return multipe values or structure

Question

There are some problems thatconfuse me:

1. The callee function needs return a structure, but there is not a structure statment in caller function. If i have to write the declaration in the calling function，it can not be called packaging function.

2. If i return a structure pointer by callee function, but the structure is in the stack of the called function and will be destroyed after the end, which is not safe. Sometimes i get some warning or even wrong!

3. I have a limited ideas but it not good. I put the structure into the heap by malloc and return the void*pointer. But this gave birth to a new problem ：after each call to this function, in the caller, I cannot release the heap through the free() function,the complier can not identify variable name of structure pointer. I think it verey dangerous. I want when the callee function quit，it can be released by itself.

This is the first time I came to this website to ask questions and I just came into contact with c language，If there is something stupid please point it out.

I have to write the structure declaration outside. This program for judging prime number, and I want to package the founction "judging_number". I do not want to write the structure declaration when I want to call the founction "judging_number".

Please give me some help, I would be very grateful. Sorry, this is my fault. I compiled it with clang++, I saved it as *.cpp, but I wrote c code in it.

What I mean is, can I put the declaration in the called function to realize the function modularization, how can I not declare a structure before calling the function? Is there any way I can not write a declaration. Like use founction in stdio.h.It is as convenient as using the functions of the standard library. Only need to write a line of function call and pass parameters, the called function can return multiple results.

    #include <stdio.h>
    
    
    struct boundary{
            int L;
            int R;
        };boundary *range;
    
    int *get_number()
        {
            int *nPtr = (int *)malloc(sizeof(int));
            do
            {
                printf("Please enter a vaild number for judging prime number.Or enter the number 1 to quit.\r\n");
                scanf("%d", nPtr);
                if (*nPtr == 1)
                {
                    exit(1);
                }
            } while (*nPtr < 1);
    
            printf("The object is %d\r\n", *nPtr);
    
            return nPtr;
    }
    
    int judg_number(int N,boundary range){
        if (N%range.L==0&&N!=2){
            printf("The number %d is a composite number.\r\n", N);
        }
    
        else{
            printf("The number %d is a prime number.\r\n", N);
        }
    
        return 0;
        
    }
    
    boundary* get_range(int N){
    
    
        boundary *Ptr = (boundary *)malloc(sizeof(boundary));
    
        *Ptr = {2,N-1};
    
        printf("The range is between %d and %d .\r\n", Ptr->L, Ptr->R);
    
        return Ptr;
    }
    
    
    int main(int argc,char**argv,char**env){
        int*N;
        while(1){
            N=get_number();
            range=get_range(*N);
            judg_number(*N, *range);
            free(N);
            free(range);
        }
        getchar();
        getchar();
        return 0;
    }

Answer 1

You dont need dynamic memory allocation here. If you want to retun an int, retun an int. If you want to retun a stuct return a struct.

You probably want this:

#include <stdio.h>
#include <stdlib.h>

struct boundary {
  int L;
  int R;
}; 

struct boundary range;

int get_number()
{
  int n;
  do
  {
    printf("Please enter a vaild number for judging prime number.Or enter the number 1 to quit.\r\n");
    scanf("%d", &n);
    if (n == 1)
    {
      exit(1);
    }
  } while (n < 1);

  printf("The object is %d\r\n", n);

  return n;
}

int judg_number(int N, struct boundary range) {
  if (N % range.L == 0 && N != 2) {
    printf("The number %d is a composite number.\r\n", N);
  }

  else {
    printf("The number %d is a prime number.\r\n", N);
  }

  return 0;
}


struct boundary get_range(int N) {
  struct boundary b = { 2, N - 1 };
  printf("The range is between %d and %d .\r\n", b.L, b.R);
  return b;
}

int main(int argc, char** argv, char** env) {
  int N;
  while (1) {
    N = get_number();
    range = get_range(N);
    judg_number(N, range);
  }
  getchar();
  getchar();
  return 0;
}

BTW:

boundary get_range(int N) {... is invalid in C but valid in C++. In C it should be struct boundary get_range(int N) {...