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This section describes the use of interoperability tools to resolve link-time conflicts when using multiple C RTLs.
When migrating to the Compaq C RTL, multiple C RTLs will likely be needed to link an application. One C RTL might be explicitly linked against. A second C RTL might not be explicitly linked against, but brought into the link by means of a shareable image. For example, when developing a Motif program using Compaq C, the application must be linked against the Compaq C RTL and against the Motif images. Motif currently brings the VAX C RTL into the link.
Problems encountered when linking with multiple C RTLs are a result of the OpenVMS linker resolving symbol references in the image being linked by searching the transitive closure of shareable images and libraries. That is, when linking with a shareable image, the linker searches that shareable image and all shareable images referenced in that shareable image. So when linking with VAXCRTL.EXE and with an image linked with VAXCRTLG.EXE, the linker will find two instances of all the C RTL symbols (one in VAXCRTL and one in VAXCRTLG), and report a conflict.
The object libraries do not conflict with routine names, but do conflict with the global symbols. Because VAX C implements global symbols as global overlaid psects, the linker attempts to connect all the instances of a C-generated psect with the same name. For example, a reference to stdin in the user program is connected with the psect of the same name in VAXCRTL.OLB. However, a shareable image that was linked with VAXCRTL.OLB also has a psect of the same name; this results in an error because the linker cannot connect those two definitions of the psect stdin .
Three interoperability tools are provided with the Compaq C compiler and in a separate Compaq C/C++ RTL Run-Time Components kit to resolve link-time conflicts:
These tools work by hiding the conflicting symbols from one of the C RTLs being linked. Which tool is required depends on what C RTLs are used by the main application and the shareable image.
Table 1-1 shows typical C RTL conflicts and the interoperability tool required to resolve it. In the table, VAXCRTL.EXE refers to either VAXCRTL.EXE or VAXCRTLG.EXE.
| Linker Message | Type of Conflict | Tool Needed |
|---|---|---|
| LINK-E-MULSHRPSC | VAXCRTL.OLB/VAXCRTL.EXE | VAXC$LCL.OPT |
| LINK-E-SHRPSCLNG | VAXCRTL.OLB/DECCRTL.OLB | VAXC$LCL.OPT |
|
LINK-E-MULSHRPSC,
LINK-E-SHRPSCLNG |
DECCRTL.OLB/VAXCRTL.EXE | VAXC$LCL.OPT |
| None. | DECCRTL.OLB/DECC$SHR.EXE | DECC$EMPTY |
| LINK-W-MULDEF | VAXCRTL.EXE/VAXCRTLG.EXE | VAXC$EMPTY |
| LINK-W-MULDEF | VAXC2DECC.EXE/VAXCRTL.EXE | VAXC$EMPTY |
VAXC$LCL.OPT is required when building any shareable image linked with the VAX C RTL object library or Compaq C RTL object library.
If the shareable image is built without using VAXC$LCL.OPT, the C RTL global symbols are visible in the shareable image and cause linker conflicts when users of the image link against it. For example:
%LINK-E-MULSHRPSC, psect C$$TRNS_VALUES defined in
shareable image IMAGE1.EXE; is multiply defined in
shareable image SYS$LIBRARY:VAXCRTL.EXE;1
-LINK-E-NOIMGFIL, image file not created
|
In this example, the shareable image IMAGE1 uses VAXCRTL.OLB, and the image being linked uses VAXCRTL.EXE. For a successful link, relink the shareable image using VAXC$LCL.OPT:
$ LINK/SHARE IMAGE1.OBJ, IMAGE1.OPT/OPTIONS, SYS$LIBRARY:VAXCRTL/LIBRARY, - _$ SYS$LIBRARY:VAXC$LCL.OPT/OPTIONS |
The following message also indicates a conflict involving the VAX C RTL object library:
%LINK-E-SHRPSCLNG, Psect STDIN has length of 8
in module C$EXTERNDATA file SYS$LIBRARY:DECCRTL.OLB;2
which exceeds length of 4 in shareable image IMAGE1.EXE;
-LINK-E-NOIMGFIL, image file not created
|
In this example, the shareable image IMAGE1 uses VAXCRTL.OLB, and the image being linked uses DECCRTL.OLB. For a successful link, relink the shareable image using VAXC$LCL.OPT.
If the shareable image cannot be relinked (as in the case of a third-party shareable image), then the interoperability tool can be applied to the main image. If the main image is being linked against DECCRTL.OLB, then apply VAXC$LCL.OPT to the link of the main image.
If the main image is being linked against VAXCRTL.EXE, the only
solution is to get the shareable image fixed, because applying any of
the interoperability tools to the link of the main image will result in
an unsuccessful link.
1.3.2.2 Using VAXC$EMPTY.EXE
Use VAXC$EMPTY.EXE to link a main application with both VAXC2DECC.EXE (or VAXCG2DECC.EXE) and a shareable image linked with VAXCRTL.EXE (or VAXCRTLG.EXE). Using VAXC$EMPTY.EXE hides all the global symbols in the VAXCRTL*.EXE shareable image to prevent conflicts with VAXC2DECC.EXE or VAXCG2DECC.EXE.
Also use VAXC$EMPTY.EXE to link an application with both VAXCRTL.EXE and a shareable image linked with VAXCRTLG.EXE (or vice versa).
When there is a conflict between C RTL shareable images, the linker produces large numbers of messages similar to the following:
%LINK-W-MULDEF, symbol ACOS multiply defined
in module VAXCRTL file SYS$COMMON:[SYSLIB]VAXCRTL.EXE;18
|
In this example, the shareable image is linked with VAXCRTL.EXE, and the main program is linked with VAXC2DECC.EXE.
The solution is to define the VAXCRTL logical to point to VAXC$EMPTY.EXE before linking the main program:
$ DEFINE/USER VAXCRTL SYS$LIBRARY:VAXC$EMPTY.EXE $ LINK/EXEC=MAIN_IMAGE MAIN_PROG,OBJ1,OBJ2,...,SYS$INPUT:/OPTIONS IMAGE1/SHARE VAXCRTL/SHARE [Ctrl/Z] |
Note the following about this solution:
Follow the same process when linking against VAXCRTLG.EXE by defining
the VAXCRTLG logical to point to VAXC$EMPTY.EXE.
1.3.2.3 Using DECC$EMPTY.EXE
The DECC$EMPTY.EXE interoperability tool allows a program to use the Compaq C object library even when the program links with a shareable image that was linked with DECC$SHR.EXE.
If DECC$EMPTY.EXE is not used during the link, all Compaq C RTL references from the main program will be resolved in DECC$SHR.EXE, not in the object library. There is no linker message that indicates this fact.
For example, if IMAGE1 is linked against DECC$SHR, and the following link is performed, then the main image will not contain any Compaq C RTL object modules. All C RTL references from the main progam are resolved in DECC$SHR:
$ LINK/EXEC=MAIN_IMAGE MAIN_PROG,OBJ1,...,SYS$INPUT:/OPTIONS IMAGE1/SHARE SYS$LIBRARY:DECCRTL/LIBRARY [Ctrl/Z] |
By defining the DECC$SHR logical to point to DECC$EMPTY.EXE immediately before the link, all references to C RTL symbols from the main program are resolved in the Compaq C RTL object library. For example:
$ DEFINE/USER DECC$SHR SYS$LIBRARY:DECC$EMPTY.EXE $ LINK/EXEC=MAIN_IMAGE MAIN_PROG,OBJ1,...,SYS$INPUT:/OPTIONS IMAGE1/SHARE SYS$LIBRARY:DECCRTL/LIBRARY |
Note the following about this solution:
The following examples show the different ways you might want to link Compaq C only or Compaq C++ only programs with the Compaq C RTL on OpenVMS VAX systems:
$ CC/DECC/PREFIX_LIBRARY_ENTRIES=ALL_ENTRIES PROG1 $ LINK PROG1 |
$ CC/DECC/PREFIX_LIBRARY_ENTRIES=ALL_ENTRIES PROG1 $ LINK/NOSYSSHR PROG1, SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=CMA$TIS $ LINK/NOSYSSHR PROG1, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=(CMA$TIS,CMA$TIS_VEC) (OPENVMS V7.3 AND HIGHER) |
$ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ LINK PROG1, MYLIB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY |
$ CC/DECC/NOPREFIX_LIBRARY_ENTRIES/FLOAT=G_FLOAT PROG1 $ LINK PROG1, MYLIB/LIBRARY, SYS$LIBRARY:DECCRTLG.OLB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY |
$ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ LINK/NOSYSSHR PROG1, MYLIB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY |
You might have programs that combine VAX C and Compaq C (or Compaq C++) code. The following examples show different ways to link such programs with the Compaq C RTL on OpenVMS VAX systems. These examples correspond to the examples in Section 1.3.3.
$ CC/DECC PROG1 $ CC/VAXC PROG2 $ LINK PROG1, PROG2, TT:/OPTIONS SYS$LIBRARY:VAXC2DECC.EXE/SHARE [Ctrl/Z] |
$ CC/DECC PROG1 $ CC/VAXC PROG2 $ LINK/NOSYSSHR PROG1, PROG2, SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=CMA$TIS |
$ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ CC/VAXC PROG2 $ LINK PROG1, PROG2, MYLIB/LIBRARY, - _$SYS$LIBRARY:DECCRTL.OLB/LIBRARY/INCL=CMA$TIS |
$ CC/DECC/NOPREFIX_LIBRARY_ENTRIES PROG1 $ CC/VAXC PROG2 $ LINK/NOSYSSHR PROG1, PROG2, MYLIB/LIBRARY, - _$ SYS$LIBRARY:DECCRTL.OLB/LIBRARY /INCL=CMA$TIS |
This section applies to programs running on OpenVMS VAX Version 6.0 or higher.
For programs that currently link with the VAX C RTL object libraries using the /NOSYSSHR qualifier, you must specify /INCLUDE=CMA$TIS for the object library. Otherwise, several symbols will be undefined and the resulting image will not execute. In order to add this qualifier, you cannot use the LNK$LIBRARY logicals to link with the VAX C RTL object libraries. You must use a linker options file or list the VAX C RTL object libraries on the command line. For example:
$ LINK/NOSYSSHR PROG1, SYS$LIBRARY:VAXCRTL.OLB/LIBRARY/INCLUDE=CMA$TIS |
After learning how to link object modules and include header files, you
must learn how to reference Compaq C functions in your program.
The remaining chapters in this manual provide detailed descriptions of
the Compaq C RTL functions.
1.4.1 Function Prototypes
In all chapters, the syntax describing each function follows the standard convention for defining a function. This syntax is called a function prototype (or just prototype). The prototype is a compact representation of the order of a function's arguments (if any), the types of the arguments, and the type of the value returned by a function. The use of prototypes is recommended.
If the return value of the function cannot be easily represented by a C data-type keyword, look for a description of the return values in the explanatory text. The prototype descriptions provide insight into the functionality of the function. These descriptions may not describe how to call the function in your source code.
For example, consider the prototype for the feof function:
|
#include <stdio.h> int feof(FILE *file_ptr); |
This syntax shows the following information:
To use feof in a program, include <stdio.h> anywhere before the function call to feof , as in the following example:
#include <stdio.h> /* Include Standard I/O */
main()
{
FILE *infile; /* Define a file pointer */
.
.
. /* Call the function feof */
while ( ! feof(infile) ) /* Until EOF reached */
{ /* Perform file operations */
.
.
.
}
}
|
Since some library functions take a varying number of parameters, syntax descriptions for function prototypes adhere to the following conventions:
Consider the printf syntax description:
|
#include <stdio.h> int printf(const char *format_specification, ...); |
The syntax description for
printf
shows that you can specify one or more optional parameters. The
remaining information about
printf
parameters is in the description of the function.
1.4.3 UNIX Style File Specifications
The Compaq C RTL functions and macros often manipulate files. One of the major portability problems is the different file specifications used on various systems. Since many C applications are ported to and from UNIX systems, it is convenient for all compilers to be able to read and understand UNIX system file specifications.
The following file specification conversion functions are included in the Compaq C RTL to assist in porting C programs from UNIX systems to OpenVMS systems:
These DECC$ routine names replace the SHELL$ routine names previously available with the VAX C RTL. |
The advantage of including these file specification conversion functions in the Compaq C RTL is that you do not have to rewrite C programs containing UNIX system file specifications. Compaq C can translate most valid UNIX system file specifications to OpenVMS file specifications.
The Compaq C RTL cannot translate UNIX file specifications with more than one period character (.). If the UNIX file specification contains a period, all slash characters (/) must precede that period. |
Please note the differences between the UNIX system and OpenVMS file specifications, as well as the method used by the RTL to access files. For example, the RTL accepts a valid OpenVMS specification and most valid UNIX file specifications, but the RTL cannot accept a combination of both. Table 1-2 shows the differences between UNIX system and OpenVMS system file specification delimiters.
| Description | OpenVMS System | UNIX System |
|---|---|---|
| Node delimiter | :: | !/ |
| Device delimiter | : | / |
| Directory path delimiter | [ ] | / |
| Subdirectory delimiter | [ . ] | / |
| File extension delimiter | . | . |
| File version delimiter | ; | Not applicable |
For example, Table 1-3 shows the formats of two valid specifications and one invalid specification.
| System | File Specification | Valid/Invalid |
|---|---|---|
| OpenVMS | BEATLE::DBA0:[MCCARTNEY]SONGS.LIS | Valid |
| UNIX | beatle!/usr1/mccartney/songs.lis | Valid |
| --- | BEATLE::DBA0:[MCCARTNEY.C]/songs.lis | Invalid |
When Compaq C translates file specifications, it looks for both OpenVMS and UNIX system file specifications. Consequently, there may be differences between how Compaq C translates UNIX system file specifications and how UNIX systems translate the same UNIX file specification.
For example, if the two methods of file specification are combined, as in Table 1-3, Compaq C RTL can interpret [MCCARTNEY.C]/songs.lis as either [MCCARTNEY]songs.lis or [C]songs.lis. Therefore, when Compaq C encounters a mixed file specification, an error occurs.
UNIX systems use the same delimiter for the device name, the directory names, and the file name. Due to the ambiguity of UNIX file specifications, Compaq C may not translate a valid UNIX system file specification according to your expectations.
For instance, the OpenVMS system equivalent of /bin/today can be either [BIN]TODAY or [BIN.TODAY]. Compaq C can make the correct interpretation only from the files present. If a file specification conforms to UNIX system file name syntax for a single file or directory, it is converted to the equivalent OpenVMS file name if one of the following conditions is true:
In the UNIX system environment, you reference files with a numeric file descriptor. Some file descriptors reference Standard I/O devices; some descriptors reference actual files. If the file descriptor belongs to an unopened file, the Compaq C RTL opens the file. Compaq C equates file descriptors with the following OpenVMS logical names:
| File Descriptor | OpenVMS Logical | Meaning |
|---|---|---|
| 0 | SYS$INPUT | Standard input |
| 1 | SYS$OUTPUT | Standard output |
| 2 | SYS$ERROR | Standard error |
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