ldopen.3x

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH ldopen 3x RISC
.SH Name
ldopen, ldaopen, ldreadst \- open a common object file for reading
.SH Syntax
.nf
.ta \w'\s-1LDFILE\s+1\ \ \ 'u
.B #include <stdio.h>
.B #include <filehdr.h>
.B #include <syms.h>
.B #include <ldfcn.h> 
.PP
.BR "\s-1LDFILE\s+1 \(**ldopen (" "filename, ldptr" )
.BR "char \(**" filename ;
.BR "\s-1LDFILE\s+1 \(**" ldptr ;
.PP
.BR "\s-1LDFILE\s+1 \(**ldaopen (" "filename, oldptr" )
.BR "char \(**" filename ;
.BR "\s-1LDFILE\s+1 \(**" oldptr ;
.PP
.BR "\s-1ldreadst\s+1 (" "ldptr, flags")
.BR "\s-1LDFILE\s+1 \(**" ldptr;
.BR "\s-1int" flags;
.fi
.DT
.SH Description
The 
.PN ldopen
and
.PN ldclose
functions provide uniform access to simple object files and
to object files that are members of archive files.
An archive
of common object files can be processed as if it is a series of
simple common object files.
.PP
If 
.I ldptr
has the value null, 
.PN ldopen
opens
.IR filename ,
allocates and initializes the
.B \s-1LDFILE\s+1
structure, and returns a pointer to
the structure to the calling program.
.PP
If
.I ldptr
is valid and
.BI \s-1TYPE\s+1( ldptr )
is the archive magic number,
.PN ldopen
reinitializes the
.BR \s-1LDFILE\s+1 " structure"
for the next archive member of
.IR filename .
.PP
The 
.PN ldopen
and
.PN ldclose
functions work in concert.  The
.PN ldclose
function returns failure only when only when
.BI \s-1TYPE\s+1( ldptr )
is the archive magic number and there is another file in the archive
to be processed.
Only then should
.PN ldopen
be called with the current value of
.IR ldptr .
In all other cases, but especially when a new
.I filename
is opened,
.PN ldopen
should be called with a null
.I ldptr
argument.
.PP
The following is a prototype for the use of 
.PN ldopen
and
.ldclose:
.EX
/* for each filename to be processed*/
.PP
ldptr = \s-1NULL\s+1;
do
	if ( (ldptr = ldopen(filename, ldptr)) != \s-1NULL\s+1 )

	{
		/* check magic number */
		/* process the file */
	}
} while (ldclose(ldptr) == \s-1FAILURE\s+1 );
.EE
.PP
If the value of
.I oldptr
is not
.BR \s-1NULL\s+1\*S ,
.PN ldaopen
opens
.I filename
anew and allocates and initializes a new
.B \s-1LDFILE\s+1
structure, copying the
fields from
.IR oldptr .
The 
.PN ldaopen
function returns a pointer to the new
.BR \s-1LDFILE\s+1 " structure."
This new pointer is independent of the old pointer,
.IR oldptr .
The two pointers can be used concurrently to read separate parts of
the object file.
For example,
one pointer can be used to step sequentially through the relocation 
information while the other is used to read indexed symbol table entries.
.PP
The
.PN ldopen
and
.PN ldaopen
functions open
.I filename
for reading.
If
.I filename
cannot be opened or if memory for the
.B \s-1LDFILE\s+1
structure cannot be allocated,
both functions return
.SM \fBNULL\fR.
A successful open does not ensure that the given file is a common object
file or an archived object file.
\}
.PP
The 
.PN ldopen
function causes the symbol table header and file descriptor 
table to be read.
Further access, using 
.I ldptr,
causes other appropriate sections of the symbol table to be read 
(for example, if you call 
.PN ldtbread, 
the symbols or externals are read).  To force sections for each symbol table in
memory, call 
.PN ldreadst 
with \fIST_P*\fR constants or'ed together 
from \fIst_support.h\fR.
.SH See Also
fopen(3s), ldclose(3x), ldfcn(5)