Need help in understanding c code

H

Herman.Schultz

Hi,

I see this code in vlc code. I have a question about this line:
net_Printf( VLC_OBJECT(p_access), p_sys->fd, pvs,
"Range: bytes="I64Fd"-\r\n", i_tell );

What is the meaning of "Range: bytes="I64Fd"-\r\n" ? especially I64Fd
(in double quotes)


static int Request( access_t *p_access, int64_t i_tell )
{
access_sys_t *p_sys = p_access->p_sys;
char *psz ;
v_socket_t *pvs = p_sys->p_vs;


//.....

net_Printf( VLC_OBJECT(p_access), p_sys->fd, pvs,
"Range: bytes="I64Fd"-\r\n", i_tell );

}
 
R

Richard Heathfield

(e-mail address removed) said:
Hi,

I see this code in vlc code. I have a question about this line:
net_Printf( VLC_OBJECT(p_access), p_sys->fd, pvs,
"Range: bytes="I64Fd"-\r\n", i_tell );

What is the meaning of "Range: bytes="I64Fd"-\r\n" ? especially I64Fd
(in double quotes)

It's probably a #define for "whatever the heck net_Printf uses as a
format specifier for long long int". For example, it might be:

#define I64Fd "%I64d"

or it might be

#define I64Fd "%lld"

or something else.

The string literal concatenation rule makes it all join up properly for
the compiler.
 
B

Barry Schwarz

Hi,

I see this code in vlc code. I have a question about this line:
net_Printf( VLC_OBJECT(p_access), p_sys->fd, pvs,
"Range: bytes="I64Fd"-\r\n", i_tell );

What is the meaning of "Range: bytes="I64Fd"-\r\n" ? especially I64Fd
(in double quotes)
I64Fd is not in double quotes. The expression consists of three
parts:
1 - the string literal "Range: bytes="
2 - the "token" I64Fd
3 - the string literal "-\r\n"

As RH suggested, the token I64Fd is probably a #define that is set to
some string literal (for sake of discussion, assume the literal is
"%_"). Consequently, the entire expression consists of three string
literals. When string literals abut or are separated only by white
space, the compiler automatically concatenates them together. As a
result, when the line question is compiled, the expression will the
single string literal:
"Range: bytes=%_-\r\n"

As usual, the address of the literal will be the value passed to
net_Printf.


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