Initalizing global variables to constants

maxhavoc · 06-21-2006, 08:54 AM

So, I'm working under Visual Studio 6 and I'm coding in C (I have to use stricly ANSI C for this work assignment).

I'm trying to create some global scope pointers and initailize them to constants and I keep getting the error C2099.

Code:

char* fileText = (char*)malloc(100);

Error text: error C2099: initializer is not a constant

It seems to me that '100' is about as constant as you can get. I tried making a #define and initializing to that, but that also failed. Is it just impossible to initalize dynamic memory in global scope in C? Because it works fine within a function.

itsme86 · 06-21-2006, 09:10 AM

First of all, you shouldn't cast the return value of malloc().

Secondly, it's not the value you're passing to malloc() that it's saying isn't constant; it's the return value of malloc() that it's complaining about. You can't use malloc() to initialize a global variable.

Why are you using malloc() there anyway? Why not just char fileText[100];?

maxhavoc · 06-21-2006, 09:13 AM

Don't you always need to cast the return value of malloc since it returns a void*?

How is the return of malloc not constant in global scope but is constant in function scope? Is that just an idiosyncrisy of C?

I suppose I could just make them static arrays, but I still want to know why I can't do what I was doing before

itsme86 · 06-21-2006, 09:17 AM

Variables with function scope don't need constant initializers. Global variables do.

Quote:

Don't you always need to cast the return value of malloc since it returns a void*?

Nope. That's a C++ idiom, but not C. As long as you're not compiling your program as C++ and you #include <stdlib.h> then you shouldn't get any warnings/errors if you omit the cast.

**Salem** · 06-21-2006, 11:17 AM

> char* fileText = (char*)malloc(100);
You're probably trying to do this outside the scope of any function.
Unlike C++, all C executable code has to be inside a function.

So

Code:

char* fileText;
int main ( ) {
    fileText = malloc(100);
    // rest of code
}

itsme86 · 06-21-2006, 11:21 AM

Quote:

Originally Posted by Salem

> char* fileText = (char*)malloc(100);
You're probably trying to do this outside the scope of any function.
Unlike C++, all C executable code has to be inside a function.

So

Code:

char* fileText;
int main ( ) {
    fileText = malloc(100);
    // rest of code
}

Isn't that pretty much what I said?

**Salem** · 06-21-2006, 11:25 AM

> Isn't that pretty much what I said?
Yes

06-21-2006, 08:54 AM	#1
maxhavoc Registered User Join Date: Jun 2004 Posts: 124	Initalizing global variables to constants So, I'm working under Visual Studio 6 and I'm coding in C (I have to use stricly ANSI C for this work assignment). I'm trying to create some global scope pointers and initailize them to constants and I keep getting the error C2099. Code: char* fileText = (char*)malloc(100); Error text: error C2099: initializer is not a constant It seems to me that '100' is about as constant as you can get. I tried making a #define and initializing to that, but that also failed. Is it just impossible to initalize dynamic memory in global scope in C? Because it works fine within a function.
maxhavoc is offline

06-21-2006, 09:10 AM	#2
itsme86 Gawking at stupidity Join Date: Jul 2004 Posts: 2,324	First of all, you shouldn't cast the return value of malloc(). Secondly, it's not the value you're passing to malloc() that it's saying isn't constant; it's the return value of malloc() that it's complaining about. You can't use malloc() to initialize a global variable. Why are you using malloc() there anyway? Why not just char fileText[100];? __________________ If you understand what you're doing, you're not learning anything. Ignore any "advice" esbo tries to give you. It's wrong.
itsme86 is offline

06-21-2006, 09:13 AM	#3
maxhavoc Registered User Join Date: Jun 2004 Posts: 124	Don't you always need to cast the return value of malloc since it returns a void*? How is the return of malloc not constant in global scope but is constant in function scope? Is that just an idiosyncrisy of C? I suppose I could just make them static arrays, but I still want to know why I can't do what I was doing before
maxhavoc is offline

06-21-2006, 11:17 AM	#5
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,693	> char* fileText = (char)malloc(100); You're probably trying to do this outside the scope of any function. Unlike C++, all C executable code has to be inside a function. So Code: char fileText; int main ( ) { fileText = malloc(100); // rest of code } __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

06-21-2006, 11:25 AM	#7
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,693	> Isn't that pretty much what I said? Yes __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

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