gcc的幾個妙用

gcc實質(zhì)是完成程序的編譯和鏈接，程序的編譯是指從一種文件類型轉(zhuǎn)換到另一種文件類型的過程。一個C語言程序轉(zhuǎn)換為可執(zhí)行程序的基本步驟如下：

1、編寫程序（vi，emacs等軟件）

2、程序預(yù)編譯（cpp）

3、編譯成匯編程序（cc）

4、匯編程序（as）

5、鏈接程序（ld）

其中的這些過程都已經(jīng)被gcc包含，我們在實際的編譯過程中采用了gcc main.c -o main.exe即可實現(xiàn)一個程序的編譯和鏈接。并不需要一步一步的實現(xiàn)，但是我們在分析的過程中又必須注意一個C語言文件的處理過程以及相應(yīng)的處理程序。

關(guān)于gcc的基本含義用法就不再詳細的說明了，我覺得最簡單的使用方法是通過軟件的help學(xué)習(xí)軟件。

[gong@Gong-Computer test]$ gcc --help
Usage: gcc [options] file...
Options:
-pass-exit-codes Exit with highest error code from a phase
--help Display this information
--target-help Display target specific command line options
--help={target|optimizers|warnings|params|[^]{joined|separate|undocumented}}[,...]
Display specific types of command line options
(Use -v --help to display command line options of sub-processes)
--version Display compiler version information
-dumpspecs Display all of the built in spec strings
-dumpversion Display the version of the compiler
-dumpmachine Display the compilers target processor
-print-search-dirs Display the directories in the compilers search path
-print-libgcc-file-name Display the name of the compilers companion library
-print-file-name= Display the full path to library
-print-prog-name= Display the full path to compiler component
-print-multi-directory Display the root directory for versions of libgcc
-print-multi-lib Display the mapping between command line options and
multiple library search directories
-print-multi-os-directory Display the relative path to OS libraries
-print-sysroot Display the target libraries directory
-print-sysroot-headers-suffix Display the sysroot suffix used to find headers
-Wa, Pass comma-separated on to the assembler
-Wp, Pass comma-separated on to the preprocessor
-Wl, Pass comma-separated on to the linker
-Xassembler Pass on to the assembler
-Xpreprocessor Pass on to the preprocessor
-Xlinker Pass on to the linker
-combine Pass multiple source files to compiler at once
-save-temps Do not delete intermediate files
-save-temps= Do not delete intermediate files
-no-canonical-prefixes Do not canonicalize paths when building relative
prefixes to other gcc components
-pipe Use pipes rather than intermediate files
-time Time the execution of each subprocess
-specs= Override built-in specs with the contents of
-std= Assume that the input sources are for
--sysroot= Use as the root directory for headers
and libraries
-B Add to the compilers search paths
-b Run gcc for target , if installed
-V Run gcc version number , if installed
-v Display the programs invoked by the compiler
-### Like -v but options quoted and commands not executed
-E Preprocess only; do not compile, assemble or link
-S Compile only; do not assemble or link
-c Compile and assemble, but do not link
-o Place the output into
-x Specify the language of the following input files
Permissible languages include: c c++ assembler none
none means revert to the default behavior of
guessing the language based on the files extension

Options starting with -g, -f, -m, -O, -W, or --param are automatically
passed on to the various sub-processes invoked by gcc. In order to pass
other options on to these processes the -W options must be used.

For bug reporting instructions, please see:
.

從上面的結(jié)果可以知道基本的用法。

但是還是有幾個需要注意的地方，這也是我們學(xué)習(xí)gcc時不經(jīng)常使用，但又非常有用的幾個用法。

1、采用gcc實現(xiàn)預(yù)編譯，預(yù)編譯可以實現(xiàn)代碼的檢查，特別是宏定義的檢查，通過預(yù)編譯檢查實際的代碼是否出錯，這是非常有用的檢查方式。

由于預(yù)編譯以后宏定義被擴展了，這時對源碼的分析就能找出代碼宏定義等是否存在錯誤，特別時一些不容易發(fā)現(xiàn)的錯誤。

基本的實現(xiàn)形式為:gcc -E file.c > file.pre.c

[gong@Gong-Computer Example]$ vi main.c

采用重定向的方式改變輸出流，便于檢查錯誤所在。
[gong@Gong-Computer Example]$ gcc -E main.c > main.pre.c

[gong@Gong-Computer Example]$ vi main.pre.c

從上面的結(jié)果可以發(fā)現(xiàn)我們的宏已經(jīng)實現(xiàn)了擴展。通過分析宏的擴展可以分析代碼是否正確。