|C H A P T E R 2|
Using the C++ Compiler
This chapter describes how to use the C++ compiler.
The principal use of any compiler is to transform a program written in a high-level language like C++ into a data file that is executable by the target computer hardware. You can use the C++ compiler to:
This section gives you a brief overview of how to use the C++ compiler to compile and run C++ programs. See Appendix A for a full reference to the command-line options.
The basic steps for building and running a C++ program involve:
1. Using an editor to create a C++ source file with one of the valid suffixes listed in TABLE 2-1
2. Invoking the compiler to produce an executable file
3. Launching the program into execution by typing the name of the executable file
The following program displays a message on the screen:
In this example, CC compiles the source file greetings.cc and, by default, compiles the executable program onto the file, a.out. To launch the program, type the name of the executable file, a.out, at the command prompt.
Traditionally, UNIX compilers name the executable file a.out. It can be awkward to have each compilation write to the same file. Moreover, if such a file already exists, it will be overwritten the next time you run the compiler. Instead, use the -o compiler option to specify the name of the executable output file, as in the following example:
In this example, the -o option tells the compiler to write the executable code to the file greetings. (It is common to give a program consisting of a single source file the name of the source file without the suffix.)
Alternatively, you could rename the default a.out file using the mv command after each compilation. Either way, run the program by typing the name of the executable file:
The remainder of this chapter discuss the conventions used by the CC command, compiler source line directives, and other issues concerning the use of the compiler.
The general syntax of a compiler command line is as follows:
An option is an option keyword prefixed by either a dash (-) or a plus sign (+). Some options take arguments.
In general, the processing of the compiler options is from left to right, allowing selective overriding of macro options (options that include other options). In most cases, if you specify the same option more than once, the rightmost assignment overrides and there is no accumulation. Note the following exceptions:
Source files, object files, and libraries are compiled and linked in the order in which they appear on the command line.
In the following example, CC is used to compile two source files (growth.C and fft.C) to produce an executable file named growth with runtime debugging enabled:
The suffix attached to a file name appearing on the command line determines how the compiler processes the file. A file name with a suffix other than those listed in the following table, or without a suffix, is passed to the linker.
Process assembly inline-template files for inline expansion. The compiler will use templates to expand inline calls to selected routines. (Inline-template files are special assembler files. See the inline(1) man page.)
The C++ compiler accepts multiple source files on the command line. A single source file compiled by the compiler, together with any files that it directly or indirectly supports, is referred to as a compilation unit. C++ treats each source as a separate compilation unit.
Beginning with the C++ 5.1 compiler, the compiler marks a template cache directory with a string that identifies the template cache's version.
This compiler does not use the cache by default. It only uses the cache if you specify -instances=extern. If the compiler makes use of the cache, it checks the cache directory's version and issues error messages whenever it encounters cache version problems. Future C++ compilers will also check cache versions. For example, a future compiler that has a different template cache version identification and that processes a cache directory produced by this release of the compiler might issue an error that is similar to the following message:
Similarly, the compiler issues an error if it encounters a cache directory that was produced by a later version of the compiler.
Although the template cache directories produced by the C++ 5.0 compiler are not marked with version identifiers, the current compiler processes the 5.0 cache directories without an error or a warning. The compiler converts the 5.0 cache directories to the directory format that it uses.
The C++ 5.0 compiler cannot use a cache directory that is produced by a later release of the compiler. The C++ 5.0 compiler is not capable of recognizing format differences and it will issue an assertion when it encounters a cache directory that is produced by the C++ 5.1 compiler or by a later release.
When you upgrade your compiler, it is always good practice to clean the cache. Run CCadmin -clean on every directory that contains a template cache directory (in most cases, a template cache directory is named SunWS_cache). Alternatively, you can use rm -rf SunWS_cache. For up-to-date instructions on how to clear the template, see the article `Upgrading Your C++ Compiler' at http://forte.sun.com/s1scc/articles/index.html.
This section describes some aspects of compiling and linking programs. In the following example, CC is used to compile three source files and to link the object files to produce an executable file named prgrm.
In the previous example, the compiler automatically generates the loader object files (file1.o, file2.o and file3.o) and then invokes the system linker to create the executable program for the file prgrm.
After compilation, the object files (file1.o, file2.o,and file3.o) remain. This convention permits you to easily relink and recompile your files.
Note - If only one source file is compiled and a program is linked in the same operation, the corresponding .o file is deleted automatically. To preserve all .o files, do not compile and link in the same operation unless more than one source file gets compiled.
If the compilation fails, you will receive a message for each error. No .o files are generated for those source files with errors, and no executable program is written.
You can compile and link in separate steps. The -c option compiles source files and generates .o object files, but does not create an executable. Without the -c option, the compiler invokes the linker. By splitting the compile and link steps, a complete recompilation is not needed just to fix one file. The following example shows how to compile one file and link with others in separate steps:
Be sure that the link step lists all the object files needed to make the complete program. If any object files are missing from this step, the link will fail with "undefined external reference" errors (missing routines).
If you do compile and link in separate steps, consistent compiling and linking is critical when using the following compiler options:
If you compile any subprogram using any of these options, be sure to link using the same option as well:
In the following example, the programs are compiled using the -xcg92 compiler option. This option is a macro for -xtarget=ss1000 and expands to: -xarch=v8 -xchip=super -xcache=16/64/4:1024/64/1.
If the program uses templates, it is possible that some templates will get instantiated at link time. In that case the command line options from the last line (the link line) will be used to compile the instantiated templates.
The compilation, linking, and execution of 64-bit objects is supported only in a V9 SPARC, Solaris 8 operating system with a 64-bit kernel running. Compilation for 64-bits is indicated by the -xarch=v9, -xarch=v9a, and -xarch=v9b options.
You can use the -verbose option to display helpful information while compiling a program, such as the names and version numbers of the programs that it invokes and the command line for each compilation phase.
Any arguments on the command line that the compiler does not recognize are interpreted as linker options, object program file names, or library names.
The basic distinctions are:
In the following example, note that -bit is not recognized by CC and the option is passed on to the linker (ld), which tries to interpret it. Because single letter ld options can be strung together, the linker sees -bit as -b -i -t, all of which are legitimate ld options. This might not be what you intend or expect:
In the next example, the user intended to type the CC option -fast but omitted the leading dash. The compiler again passes the argument to the linker, which in turn interprets it as a file name:
The C++ compiler package consists of a front end, optimizer, code generator, assembler, template pre-linker, and link editor. The CC command invokes each of these components automatically unless you use command-line options to specify otherwise.
Because any of these components may generate an error, and the components perform different tasks, it may be helpful to identify the component that generates an error. Use the -v and -dryrun options to help with this.
As shown in the following table, input files to the various compiler components have different file name suffixes. The suffix establishes the kind of compilation that is done. Refer to TABLE 2-1 for the meanings of the file suffixes.
This section discusses information about preprocessing directives that is specific to the C++ compiler.
The preprocessor keyword pragma is part of the C++ standard, but the form, content, and meaning of pragmas is different for every compiler. See Appendix B for a list of the pragmas that the C++ compiler recognizes.
The C++ compiler accepts #define preprocessor directives of the following form.
If the macro parameter list ends with an ellipsis, an invocation of the macro is allowed to have more arguments than there are macro parameters. The additional arguments are collected into a single string, including commas, that can be referenced by the name __VA_ARGS__ in the macro replacement list. The following example demonstrates how to use a variable-argument-list macro.
which results in the following:
TABLE A-3 in the appendix shows the predefined macros. You can use these values in such preprocessor conditionals as #ifdef.The +p option prevents the automatic definition of the sun, unix, sparc, and i386 predefined macros.
The #error directive no longer continues compilation after issuing a warning. The previous behavior of the directive was to issue a warning and continue compilation. The new behavior, consistent with other compilers, is to issue an error message and immediately halt compilation. The compiler quits and reports the failure.
The amount of memory a compilation requires depends on several parameters, including:
On the SPARC platform, if the optimizer runs out of memory, it tries to recover by retrying the current procedure at a lower level of optimization. The optimizer then resumes subsequent routines at the original level specified in the -xOlevel option on the command line.
If you compile a single source file that contains many routines, the compiler might run out of memory or swap space. If the compiler runs out of memory, try reducing the level of optimization. Alternately, split multiple-routine source files into files with one routine per file.
The swap -s command displays available swap space. See the swap(1M) man page for more information.
The following example demonstrates the use of the swap command:
Use mkfile(1M) and swap (1M) to increase the size of the swap space on a workstation. (You must become superuser to do this.) The mkfile command creates a file of a specific size, and swap -a adds the file to the system swap space:
Compiling very large routines (thousands of lines of code in a single procedure) at -xO3 or higher can require a large amount of memory. In such cases, performance of the system might degrade. You can control this by limiting the amount of virtual memory available to a single process.
To limit virtual memory in an sh shell, use the ulimit command. See the sh(1) man page for more information.
The following example shows how to limit virtual memory to 16 Mbytes:
In a csh shell, use the limit command to limit virtual memory. See the csh(1) man page for more information.
The next example also shows how to limit virtual memory to 16 Mbytes:
Each of these examples causes the optimizer to try to recover at 16 Mbytes of data space.
The limit on virtual memory cannot be greater than the system's total available swap space and, in practice, must be small enough to permit normal use of the system while a large compilation is in progress.
Be sure that no compilation consumes more than half the swap space.
With 32 Mbytes of swap space, use the following commands:
In an sh shell:
In a csh shell:
The best setting depends on the degree of optimization requested and the amount of real memory and virtual memory available.
A workstation should have at least 64 megabytes of memory; 128 Mbytes are recommended.
To determine the actual real memory, use the following command:
You can simplify complicated compiler commands by defining special shell aliases, using the CCFLAGS environment variable, or by using make.
The following example defines an alias for a command with frequently used options.
The next example uses the alias CCfx.
The command CCfx is now the same as:
You can specify options by setting the CCFLAGS variable.
The CCFLAGS variable can be used explicitly in the command line. The following example shows how to set CCFLAGS (C Shell):
The next example uses CCFLAGS explicitly.
When you use make, if the CCFLAGS variable is set as in the preceding example and the makefile's compilation rules are implicit, then invoking make will result in a compilation equivalent to:
CC -xO2 -xsb files...
The make utility is a very powerful program development tool that you can easily use with all Sun compilers. See the make(1S) man page for additional information.
When you are using the implicit compilation rules of the makefile (that is, there is no C++ compile line), the make program uses CCFLAGS automatically.
You can incorporate different file suffixes into C++ by adding them to your makefile. The following example adds .cpp as a valid suffix for C++ files. Add the SUFFIXES macro to your makefile:
SUFFIXES: .cpp .cpp~
(This line can be located anywhere in the makefile.)
Add the following lines to your makefile. Indented lines must start with a tab.
The standard library file names do not have .h suffixes. Instead, they are named istream, fstream, and so forth. In addition, the template source files are named istream.cc, fstream.cc, and so forth.