question about c functions

**LowLife** · 11-16-2005

Hi all, I've got a little question about functions in c, I wrote a whole "program" (well, not so big, but still), which I am not going to post here, it's not important, instead I will try to explain my problem with a little example

assume you've got this:

Code:

int number = 4;           //length of word string
char word[number];       //declaration of word

//later in the program, you specify the value f.e.

//here comes input code for first char
word[0] = 'f'
//here comes input code for second char
word[1] = 'o'
//...
word[2] = 'o'
//...
word[3] = '\0'

now, in my program, the input is done by the user, character by character (it's on my psp)
my question is, can I put the whole thing into a function, which first asks the user to input char by char, and then returns the whole string
the point is being able to put the function into a header file, so I can keep my code clean

**itsme86** · 11-16-2005

I think the problem you're running into is returning the address of a local variable. You can't do something like:

Code:

char *func(void)
{
  char word[] = "foo";

  return word;
}

For the exact same reason you can't do this:

Code:

int *func(void)
{
  int a;

  return &a;
}

Local variables in a function are created on the stack and as soon as that function returns the stack space allocated for that function becomes invalid.

A few solutions:
- Declare word as static (e.g. static char word[] = "foo"

This changes the lifetime of word from until-the-function-returns to until-the-program-ends.
- Pass word in from the calling function instead of declaring it within the function.
- Use dynamic memory allocation to get the memory for word. The calling function will need to free() the memory when it's done with it.
- Declare word as a global variable.

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