Return array from function -conflicting types for

Question

My purpose is to create an array in a function and then return it to the main function. I was recommended to allocate the array on the heap in the function (otherwise popped from the stack as soon as its returned).

The code is shown below:

 #include <stdlib.h>
 int main() {

    double *v1 = myFunction();

    return 0;
 }



 double *myFunction() {
   return malloc(10*sizeof(double));
 }

When I compile this code with gcc I get the following error-message:

 ..\src\main3.c:38:9: error: conflicting types for 'myFunction'

What is wrong with this code? Why do I get this compilation error?

Answer 1

Provide myFunction() 's prototype before using it, that is before main() like so:

double * myFunction();

int main(void)
{
  ...

If not doing so, the compiler assumes type int for myFunction() when seeing it for the first time.

Than later it finds it to be declared as double * (being different from int ) which then provokes the error.

Turning on all warnings would have pointed you to using a function without prototype. Use -Wall -Wextra -pedantic to turn on most of gcc's warnings.

---

Another issue is that declaring a function without any arguments specified leaves it open what to pass on calling the function:

double * myFunction();

If a function should be specfied to not have any arguments specify void as argument:

double * myFunction(void);

The same for how your code defines main() . It shall be:

int main(void);

or either be

int main(int argc, char ** argv);

Answer 2

1) Add prototype of myfunction at the starting like following or

double *myFunction();
 int main() {
    double *v1 = myFunction();
    return 0;
 }
 double *myFunction() {
   return malloc(10*sizeof(double));
 }

2). or define the functionBody before it is called

 double *myFunction() {
   return malloc(10*sizeof(double));
 }

 int main() {
    double *v1 = myFunction();
    return 0;
 }

However, first solution is preferable.

Answer 3

Your code is almost fine, there's only one little but blocking error, you are trying to use myFunction before the symbol is defined, all you have to do is :

#include <stdlib.h>
double *myFunction() { // myFunction should be declared before it's used
    return malloc(10*sizeof(double));
}

int main() {
    double *v1 = myFunction();
    return 0;
}

The the open C book states "All identifiers in C need to be declared before they are used. This is true for functions as well as variables." the beauty in C is that you can do can do amazing stuff like this piece of code , but you should follow some guidelines, read the open C book!.

Cheers.

Answer 4

尝试这个..

 return (double*) malloc(10*sizeof(double));