[ECOS] programming technic about the macro?

[ECOS] programming technic about the macro?

[Qiang Huang]

Hi all:
    I have looked into the IO support function and found the following:

for example(ARM):

#define HAL_READ_UINT16_STRING( _register_, _buf_, _count_)             \
    CYG_MACRO_START                                                     \
    cyg_count32 _i_;                                                    \
    for( _i_ = 0; _i_ < (_count_); _i_++)                               \
        (_buf_)[_i_] = ((volatile CYG_WORD16 *)(_register_))[_i_];      \
    CYG_MACRO_END


in the macro the tempory variable **_i_** has been declared, so if this
macro has been called twice inside one function will it cause any variable
redefinition (_i_)  problem?e.g.

main()
{
   HAL_READ_UINT16_STRING();
   HAL_READ_UINT16_STRING();
}


Thank you.



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Re: [ECOS] programming technic about the macro?

[Gary Thomas]

On Mon, 2002-10-28 at 15:12, Qiang Huang wrote:
> Hi all:
>     I have looked into the IO support function and found the following:
> 
> for example(ARM):
> 
> #define HAL_READ_UINT16_STRING( _register_, _buf_, _count_)             \
>     CYG_MACRO_START                                                     \
>     cyg_count32 _i_;                                                    \
>     for( _i_ = 0; _i_ < (_count_); _i_++)                               \
>         (_buf_)[_i_] = ((volatile CYG_WORD16 *)(_register_))[_i_];      \
>     CYG_MACRO_END
> 
> 
> in the macro the tempory variable **_i_** has been declared, so if this
> macro has been called twice inside one function will it cause any variable
> redefinition (_i_)  problem?e.g.
> 
> main()
> {
>    HAL_READ_UINT16_STRING();
>    HAL_READ_UINT16_STRING();
> }
> 

No - look more carefully and you'll see that CYG_MACRO_START generates
an opening brace "{" and CYG_MACRO_END a closing brace "}".  So the
HAL_READ_UINT16_STRING macro defines a separate scope for "_i_"

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Re: [ECOS] programming technic about the macro?

[sandeep]

Hi Qiang,


> #define HAL_READ_UINT16_STRING( _register_, _buf_, _count_)             \
>     CYG_MACRO_START                                                     \
>     cyg_count32 _i_;                                                    \
>     for( _i_ = 0; _i_ < (_count_); _i_++)                               \
>         (_buf_)[_i_] = ((volatile CYG_WORD16 *)(_register_))[_i_];      \
>     CYG_MACRO_END
> 
> in the macro the tempory variable **_i_** has been declared, so if this
> macro has been called twice inside one function will it cause any variable
> redefinition (_i_)  problem?e.g.
> 
> main()
> {
>    HAL_READ_UINT16_STRING();
>    HAL_READ_UINT16_STRING();
> }

There won't be any problem because in the code in question, the scopes of two 
_i_ are different.

if you look at packages/infra/current/include/cyg_type.h, you shall find --

#define CYG_MACRO_START do {
#define CYG_MACRO_END } while (0)


-- 
regards
sandeep
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