#93753 - spencer723 - Fri Jul 21, 2006 12:31 am
For some reason when I try this:
| Code: |
dmaCopy(myBG_bin, BG_TILE_RAM_SUB(0), myBG_bin_size);
|
I get the error:
| Code: |
error: invalid conversion from 'int' to 'void*'
error: initializing argument 2 of 'void dmaCopy(const void*, void*, uint32)'
|
Anyone have any idea what's going on? It's worked before but now it won't compile
#93755 - tepples - Fri Jul 21, 2006 12:49 am
How is BG_TILE_RAM_SUB() defined? And did it "work[] before" in C when you are now using C++?
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#93756 - spencer723 - Fri Jul 21, 2006 1:05 am
I'm afraid I'm not following you tepples :S
#93757 - tepples - Fri Jul 21, 2006 1:08 am
- The expression BG_TILE_RAM_SUB(0) looks like the evaluation of a preprocessor macro. In which header file is this macro defined?
- Are you using the C language, or are you using the C++ language?
- Was the program where the code "worked before" written in the C language, or was it written in the C++ language?
- Exactly what do you not understand about these questions?
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#93767 - spencer723 - Fri Jul 21, 2006 4:11 am
1. It is defined in <nds/arm9/video.h>
2. C++
3. Same program, different Makefile
4. Just the wording of your question caught me
#93771 - tepples - Fri Jul 21, 2006 4:47 am
| spencer723 wrote: |
| 1. It is defined in <nds/arm9/video.h> |
Then the answer to "How is it defined?" is
| Code: |
| #define BG_TILE_RAM_SUB(base) (((base)*0x4000) + 0x06200000) |
Notice the lack of a cast to any pointer type here.
ISO C++ is much stricter about pointer casting than C ever was:
| Code: |
// In your code, you'll need to replace this expression
BG_TILE_RAM_SUB(base)
// with this expression
reinterpret_cast<void *>(BG_TILE_RAM_SUB(base)) |
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#93797 - parrot_ - Fri Jul 21, 2006 9:18 am
I'm sure just adding (void*) works too.
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#93820 - spencer723 - Fri Jul 21, 2006 1:52 pm
Ahh, I knew I forgot something, thanks!
#93878 - tepples - Fri Jul 21, 2006 7:51 pm
| parrot_ wrote: |
| I'm sure just adding (void*) works too. |
Right, but C style casting will likely be dropped in future versions of C++.
Synonyms:
| Code: |
reinterpret_cast<type>(expr) // C++ way
(type) expr // C way
// The portable way
#ifdef __cplusplus
#define CAST(type, expr) (reinterpret_cast<type>(expr))
#else
#define CAST(type, expr) ((type)(expr))
#endif |
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#93882 - Sausage Boy - Fri Jul 21, 2006 8:07 pm
I don't think C style casting will be dropped, as it will brake almost every larger program in existance. That's just stupid.
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#93905 - PeterM - Fri Jul 21, 2006 10:22 pm
The reason C++ has extra casts is to make the purpose of the code clear to the reader.
static_cast is for conversions which are somewhat sane (base* -> subclass*, float -> int etc)
reinterpret_cast is the dangerous one (int <-> ptr etc)
dynamic_cast does runtime error checking for silly casts (cat* -> sheep* etc)
const_cast is for casting away consts (indicative of lazy programming somewhere)
What I do is just use static_cast, and the compiler will tell me if that's not good enough.
Whereas C just has a plain old cast, and you've go to figure out WTF the coder was thinking yourself.
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#93919 - HyperHacker - Sat Jul 22, 2006 12:06 am
...Which is where comments come in.
Isn't C++ supposed to be backward compatible anyway?
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#93956 - tepples - Sat Jul 22, 2006 2:29 am
The C++ language is not a strict superset of the C language. It's a superset of a fairly comprehensive subset of the C language. If you have a C program with variables called 'throw', 'xor', 'template', or 'new', it is not a valid C++ program.
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