The GCC Compiler
CodeWarrior provides a proprietary compiler that supports C and C++ and includes support for Altivec. CodeWarrior and Xcode C and C++ libraries are discussed in “C and C++ Libraries.”
Xcode uses the open-source GNU C Compiler, or GCC. When you compile C, C++, Objective-C, or Objective-C++ code in Xcode, you’re using GCC. The default version of GCC for Xcode 2.2 is 4.0. For versions of Xcode earlier than Xcode 2.0, the default version of GCC is 3.3. If necessary, you can choose from the the available GCC versions by selecting a target in the project window, opening an inspector window, and selecting the Rules pane. There you can use the pop-up menus to view the current system rules and to add rules for which compiler to use for C, C++, and other types of files in that target. For related information, see “More on GCC Compiler Versions.”
Note: Versions of the Xcode Tools package prior to Xcode 2.0 also included GCC versions 2.95 and 3.1; these versions are not included with subsequent versions of the tools.
When you import a CodeWarrior project, the rule for processing C files is left unchanged. This means that C files are compiled with the current system version of GCC, which depending on the system, is either 3.3 or 4.0. This document assumes that you will use version 4.0 to build your imported project.
Compile speed has improved dramatically in GCC 3.3 and 4.0, but does not yet quite equal CodeWarrior. However, Xcode sports features such as distributed and multiprocessor builds, where each compile is handled by a separate CPU, even on separate machines. These features can dramatically reduce build time for large projects. Xcode also provides additional features to improve the overall development process, including ZeroLink and Fix and Continue, described in “Some Special Features of Xcode.”
Note: You can view the full compile commands, as well as other detailed build information, in a display area in the Build Results window. You can open the Build Results window with Build > Build Results. You can open the display area by clicking the build log button at the bottom of the window's topmost pane.
Figure 1-3 shows some GCC build settings in an inspector window for an Xcode target. Build settings in the Xcode user interface are converted to command-line options to GCC when you compile your source code. If you want to use a feature of GCC that isn’t available in the Xcode user interface, you can add flags to the Other C Flags setting. To view this setting, see the detailed steps provided in “Inline ASM.” Multiple flags should be separated by spaces.
There are a number of significant differences between GCC and the CodeWarrior compiler. One that you’re likely to notice right away is that GCC has a reputation for strictness, and is likely to generate many warnings for code that may produce few warnings in CodeWarrior. Because C and C++ are very permissive languages, most of these warnings have been found to be useful over the years. Getting a compiler error or warning about suspect code can save days or even weeks of difficult debugging.
Still, you have options to reduce the number of warnings. To change the warnings for a selected target, open the inspector window, select the Build pane, and choose Warnings under GNU C/C++ Compiler in the Collections menu. You can then select any of the warning settings and see a description for it displayed beneath the list of settings, as shown in Figure 1-5.
You can also set additional GCC warnings by modifying the Other Warning Flags build setting in the Build pane.
In this section:
More on GCC Compiler Versions
Additional Compiler Information
More on GCC Compiler Versions
The C++ ABI changed between GCC 4.0 and GCC 3.3 (the default compiler for Xcode 1.5 and earlier). The GCC 3.3 compiler in turn has a different ABI than either the GCC 3.1 compiler (the default compiler for the December 2002 release of the Developer Tools) or the GCC 2.95 compiler (the default compiler for earlier releases of the Developer Tools). All your C++ code, including libraries and frameworks, must be built with the same compiler. Note that you should not use the GCC 4.0 compiler to build C++ programs for versions of Mac OS X prior to 10.3.9.
IOKit-based device drivers and other kernel extensions built with the GCC 4.0 compiler will run in Mac OS X versions 10.2 through 10.4. You must use GCC 2.95.2 for kernel extensions that need to run on Mac OS X version 10.1.
Additional Compiler Information
Additional compiler-related differences are described throughout this document, especially in the following sections:
Current documentation for GCC (through version 4.0) is available in Tools Documentation.
Last updated: 2006-10-26
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