[ECOS] process_mode question

[ECOS] process_mode question

[Slide]

In packages/language/c/libc/stdio/current/src/common/fopen.cxx fopen
is defined as the following:

 externC FILE *
 fopen( const char *filename, const char *mode ) __THROW
 {
     cyg_stdio_handle_t dev = 0;
     Cyg_ErrNo err;
     Cyg_StdioStream::OpenMode open_mode = Cyg_StdioStream::CYG_STREAM_READ;
     cyg_bool binary, append;

     // process_mode returns true on error
     if (process_mode( mode, &open_mode, &binary, &append )) {
         errno = EINVAL;
         return NULL;
     } // if

     err = cyg_stdio_open( filename, open_mode, binary, append, &dev );

     // if not found
     if (err != ENOERR) {
         errno = ENOENT;
         return NULL;
     } // if

     return fopen_inner( dev, open_mode, binary, append );

 } // fopen()


You can see that open_mode is passed into process_mode initialized to
CYG_STREAM_READ.

If I call fopen("myfile.txt", "a") process_mode will have left
open_mode as CYG_STREAM_READ and set the append parameter to true.
Then in cyg_stdio_open, it does the following:

inline Cyg_ErrNo cyg_stdio_open( const char *filename,
                                 const Cyg_StdioStream::OpenMode rw,
                                 const cyg_bool binary,
                                 const cyg_bool append,
                                 cyg_stdio_handle_t *dev)
{
    mode_t mode = 0;
    int fd;

    switch( rw )
    {
    case Cyg_StdioStream::CYG_STREAM_WRITE:
        mode = O_WRONLY|O_CREAT|O_TRUNC;
        break;
    case Cyg_StdioStream::CYG_STREAM_READ:
        mode = O_RDONLY;
        break;
    case Cyg_StdioStream::CYG_STREAM_READWRITE_NOCREATE:
        mode = O_RDWR;
        break;
    case Cyg_StdioStream::CYG_STREAM_READWRITE_CREATE:
        mode = O_RDWR|O_CREAT|O_TRUNC;
        break;
    }

    if( append )
    {
        mode |= O_APPEND;
        mode &= ~O_TRUNC;
    }

     fd = open( filename, mode );

     if( fd < 0 )
         return errno;

     *dev = fd;
     return ENOERR;
 }


by the time it gets to the call to open(), the mode is now (O_RDONLY |
O_APPEND), if its appending, shouldn't it at least start out as write?

Thanks,

slide




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Re: [ECOS] process_mode question

[Jonathan Larmour]

Slide wrote:
> In packages/language/c/libc/stdio/current/src/common/fopen.cxx fopen
> is defined as the following:
> 
>  externC FILE *
>  fopen( const char *filename, const char *mode ) __THROW
>  {
>      cyg_stdio_handle_t dev = 0;
>      Cyg_ErrNo err;
>      Cyg_StdioStream::OpenMode open_mode = Cyg_StdioStream::CYG_STREAM_READ;
>      cyg_bool binary, append;
> 
>      // process_mode returns true on error
>      if (process_mode( mode, &open_mode, &binary, &append )) {
[snip]
> You can see that open_mode is passed into process_mode initialized to
> CYG_STREAM_READ.
> 
> If I call fopen("myfile.txt", "a") process_mode will have left
> open_mode as CYG_STREAM_READ and set the append parameter to true.

Actually it doesn't quite work like that:

The relevant bit is:

    switch (mode[0]) {
    case 'r':
        *rw = Cyg_StdioStream::CYG_STREAM_READ;
        break;

    case 'a':
        *append = true;
    case 'w':
        *rw = Cyg_StdioStream::CYG_STREAM_WRITE;
        break;

    default:
        return true;
    } // switch

Note that there is no 'break;' in the 'a' case, so it drops through.

But to make this clearer for readers I'll add a /* DROPTHROUGH */ comment.

Jifl
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