Why am I unable to store the return value of the function?

Question

I am trying to return the value of a string from another function and store it as a variable. This is what I have written but I am having trouble resolving the issue.

#include "stdio.h"

void main() 
{
    printf("Hello World\n");
    char result[60];
    result = menuFunction();
}

const char* menuFunction() 
{
    return "Hello Again";
}

`result = menuFunction();`...compiler did not tell you anything? — Sourav Ghosh, May 22 '17 at 05:51
see this : http://stackoverflow.com/questions/8440816/warning-implicit-declaration-of-function you need to switch the order of declaration — Naor Tedgi, May 22 '17 at 05:52
Use `#include `. Note [What should `main()` return in C and C++?](http://stackoverflow.com/questions/204476/) too. — Jonathan Leffler, May 22 '17 at 05:53
*"...but I am having trouble resolving the issue"* What issue? — CinCout, May 22 '17 at 05:54
Another approach: `result = menuFunction();` -> `strcpy(result, menuFunction())`. That will copy the "Hello Again" into `result` — 4386427, May 22 '17 at 06:20

Sourav Ghosh · Accepted Answer · 2017-05-22T05:57:33.747

In your code, result is array type, which is not a modifiable lvalue, hence cannot be used as LHS of assignment operator.

Quoting C11, chapter §6.5.16

An assignment operator shall have a modifiable lvalue as its left operand.

and chapter §6.3.2.1, (emphasis mine)

An lvalue is an expression (with an object type other than void) that potentially designates an object; ⁶⁴⁾ if an lvalue does not designate an object when it is evaluated, the behavior is undefined. When an object is said to have a particular type, the type is specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that does not have array type, does not have an incomplete type, does not have a const-qualified type, and if it is a structure or union, does not have any member (including, recursively, any member or element of all contained aggregates or unions) with a const-qualified type.

Solution: Define result as a pointer instead.

That said,

for a hosted environment, void main() is pretty much disallowed. You should be using int main(void) to conform to the standard.
using a function (call) before the function definition or a forward declaration in place, is also disallowed. You need to define the function beforehand or have a forward declaration of the same before you use it.

Why am I unable to store the return value of the function?

1 Answers1