Error C2371: redefinition; different basic types - why?

Question

I have the following code:

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

// helping
void sortint(int numbers[], int array_size)
{
  int i, j, temp;

  for (i = (array_size - 1); i > 0; i--)
  {
    for (j = 1; j <= i; j++)
    {
      if (numbers[j-1] > numbers[j])
      {
        temp = numbers[j-1];
        numbers[j-1] = numbers[j];
        numbers[j] = temp;
      }
    }
  }
}

// exer1 - A

void sort(int** arr, int arrsize) {
    int i = 0;
    // sort....
    for(; i < arrsize; ++i) {
        sortint((*(arr+i))+1,  **(arr+i));
    }
}

// Exer1 - B

void print(int** arr, int arrsize) {
    int i = 0, j, size, *xArr;
    for(; i < arrsize; ++i) {
        size = **(arr+i);
        xArr = *(arr+i);
        printf("size: %d: ", size);
        // print elements
        for(j = 1; j <= size; ++j) printf("[%d], ", *(xArr+j));
        printf("\n");
    }
}

// Exer2:

void exera() {
    int* ptr = (int*)malloc(sizeof(int));
    if(!ptr) exit(-1);
    eb(ptr);
    free(ptr);
}

void eb(int* ptr) {
    int* arr = (int*) malloc(sizeof(int) * (*ptr));
    int i = 0;
    for(; i < *ptr; ++i) scanf("%d", arr+i);
    ec(arr, *ptr);
}

void ec(int* arr, int size) {
    int i;
    sortint(arr, size);
    for(i = 0; i < size; ++i) printf("[%d], ", *(arr+i));
}

int main() {
    // Exer1:
    int a[] = {4,3,9,6,7};
    int b[] = {3,2,5,5};
    int c[] = {1,0};
    int d[] = {2,1,6};
    int e[] = {5,4,5,6,2,1};
    int* list[5] = {a,b,c,d,e};
    sort(list, 5); // A
    print(list, 5); // B
    printf("\n\n\n\n\n");
    // Exer2:
    exera();
    fflush(stdin);
    getchar();
    return 0;
}

I get these errors:

Error   2   error C2371: 'eb' : redefinition; different basic types
source.c    56

Error   4   error C2371: 'ec' : redefinition; different basic types 
source.c    63

Warning 1   warning C4013: 'eb' undefined; assuming extern returning int    
source.c    52

Warning 3   warning C4013: 'ec' undefined; assuming extern returning int    
source.c    60

I tried to change function names - for nothing.

Why is that error is being shown? I'm using Visual C++ Express 2010.

Answer 1

You are trying to call eb and ec before they are declared or defined. Move the definition of ec before eb and both before exera. You could also forward declare your functions before you define any of them like so:

void eb(int* ptr) ;
void ec(int* arr, int size) ;

Answer 2

You call eb from exera, before eb is declared. The compiler assumes it'll return int then finds an implementation that returns void further down the file.

The most common fix is to declare your local functions at near top of your file

void eb(int* ptr);
// repeat for each other function which generates the same error

Answer 3

If you are going to place the function eb after the point at which it is called, then you need to place a prototype for it before it is called... otherwise, C will use the default prototype and then your function ends up redefining it, thus the error you received.

Alternatively, you can move the functions themselves before they are used in the source file, but that's not always possible. Placing prototypes at the top of the file or, better still, in a header file you can include anywhere you will use the functions is the best alternative.