The compiler's essential duty is to translate a computer program from one language to another, and it usually does this more than once in the a single compilation.
When compiling a program written in C, the compiler goes through several steps to translate it into machine code that can be executed on your target architecture or platform.
In general, the compiler performs the following functions on your code:
Pre-processing. The C preprocessor ("cpp") prepares your code to be sent to the actual compiler by removing comments, expanding macros, and performing a few other important steps.
Syntax checking. Does your program contain any syntactical errors? If so, the compiler will let you know, and you will have to fix them before you proceed. If it suspects some parts of your program are not correct, but it's not sure that they are actually errors, it may issue warnings, but still compile the program.
Conversion to assembly language. This is an intermediary step where your code is translated into the language of your target system's assembly language. This is pretty much the last step where your code is still readable by a human.
Assembly. Your program is assembled into the bits and bytes of object code suitable for your target platform.
Linking. The object code is linked together with the object code of any library functions specified by your program and command line options, and an executable file is created.
There are literally hundreds of options you can pass to the compiler to fine-tune how your program executes. Here we have selected some of the most useful and commonly-used options which you may need to create an executable file.
-c
Just compile the code; do not attempt to link source files. Object files will be created, which can optionally be linked later in a separate step to create an executable file.
-O[level]
Create an optimized executable. The compiler will analyze your code, and if it knows any clever tricks to speed up performance, it will implement them in the byte code. The level is an optional number, letter, or word which can specify how much optimization should be done. For instance, the GNU compiler collection allows for the options -O0 to specify minimum optimization (the default), -O1 and -O2 for intermediate levels of optimization, and -O3 for maximum optimization. -Ofast can be used as an alias for -O3, and -Og will perform optimizations that are compatible with later analysis by a debugger.Optimization requires more computation and memory, and will take longer to complete. Common optimization tricks for x86 systems include reducing instruction size to make execution less computationally expensive, implementing a dedicated register for the value zero (because zero is used so commonly in most programs), and optimizing certain multiplication and array index-scaling operations by taking advantage of the LEA ("load effective address") instruction.
-Wall
Enable "all" (all but the most esoteric) warnings when compiling. This is a good option to use regularly, as it can cue you in to any conditions which may not be errors, but which you may nonetheless want to resolve before compiling.
-ansi
Disable most (but not all) of the non-ANSI C compliant features provided by cc. To adhere to strict ANSI standards, enable this option. Doing so will ensure that your code is fully portable to be compiled on any other system.
-g
Create a debugging version of the compiled executable file. The compiler will include information in the compiled executable about which line of which source file corresponds to which function call. A debugger can later use this information to show the source code as you step through the program. Note that this creates a much larger executable file.
-D name[=value]
Defines a macro at compile time by assigning the specified value to the symbol name. When the C preprocessor is run, it will expand any instances of name to the text of value.
-Idir
Search dir for included files whose names do not begin with a slash (/) prior to searching the usual directories. The directories for multiple -I options are searched in the order specified. The preprocessor first searches for #include files in the directory containing sourcefile, and then in directories named with -I options (if any), then /usr/ucbinclude, and finally, in /usr/include.
-Ldir
Add dir to the list of directories where the compiler will look for linked libraries. This option is passed to ld and /usr/lib.
-llibrary
If linking, this options adds the indicated library to the list of libraries to be linked. For instance, if you are using functions from the C math library (libm), you would link it at compile time using the option -lm.
Be aware of your libraries' inter-dependencies and make sure to link them in the correct order on the command line; specify first any libraries which other libraries will depend on. For instance, "-lGL -lGLU" will search libGL first and then libGLU. libGLU depends on libGL, so if you reversed the order of these -l options, the program would not compile.
-M
If linking, creates a map file with the same base name as the output executable, but with the suffix .map. This map file contains a list of symbols with their addresses.
-mmodel
Specifies the memory model that the compiler and linker use. Values of model include s for "small" memory model, m for "medium", l for "large", and f for "flat" (32-bit), c for "compact", or h for "huge". Unless you're sure you require this option, you may omit it.
-o file name
The output name of the compiled executable file. If file name is not specified, the compiled executable will be named a.out.
-S
Produces assembler source code, but stops before actually assembling.
-Uname
"Undefine" any previously-defined macro named name, either in the source code or specified on the command line with -D.
The following environment variables affect the compilation process:
LANG
LC_CTYPE
LC_MESSAGES
LC_ALL
These environment variables control the way the compiler uses localization information to work with different national conventions. A common value is "en_GB.UTF-8" for English language encoded in UTF-8. If set, the LC_ALL variable overrides all other locale settings.
To view your current locale settings, use the locale command.
TMPDIR
If TMPDIR is set, it specifies the directory to use for temporary files. The compiler uses temp files to hold the output of one stage of compilation that is to be used as input to the next stage. For example, the output of the preprocessor, which is the input to the actual compiler, is stored in a temporary file during the compilation process.
COMPILER_PATH
A colon-separated list of directories, much like the PATH variable. The compiler will search this list of directories for subprograms if it can't find them using the value of GCC_EXEC_PREFIX.
LIBRARY_PATH
A colon-separated list of directories, much like PATH. When linking, the compiler will search this list of directories for linked libraries, and for special linker files it can't find using the value of GCC_EXEC_PREFIX.
Each of these variables may hold a list of directories separated by a special character, much like PATH, in which the compiler will look for header files. The special character, PATH_SEPARATOR, is target-dependent and determined at build time. For most Linux targets, PATH_SEPARATOR is a colon.
CPATH specifies a list of directories to be searched as if specified with the -I option, but after any paths given with the -I option.
C_INCLUDE_PATH, CPLUS_INCLUDE_PATH, and OBJC_INCLUDE_PATH apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with -isystem, but after any paths given with -isystem options on the command line.
In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the value of CPATH is :/special/include, that has the same effect as "-I. -I/special/include".
DEPENDENCIES_OUTPUT
If this variable is set, its value specifies how to output dependencies for make based on the non-system header files processed by the compiler. System header files are ignored in the dependency output.
The value of DEPENDENCIES_OUTPUT can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form "file target", in which case the rules are written to file file using target as the target name.
cc (運行系統的C編譯器)
cc命令運行系統的C 編譯器。
On Unix-like operating systems, the cc command runs the system's C compiler.
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1 cc 運行系統環境
2 cc 描述
3 cc 語法
4 cc 選項
5 cc 環境變量
6 cc 示例
cc 運行系統環境
Unix&Linux
cc 描述
編譯器的基本職責是將計算機程序從一種語言翻譯成另一種語言，并且通常在一次編譯中執行一次以上。
編譯用C編寫的程序時，編譯器將通過幾個步驟將其轉換為可在目標體系結構或平臺上執行的機器代碼。
通常，編譯器對您的代碼執行以下功能：
The compiler's essential duty is to translate a computer program from one language to another, and it usually does this more than once in the a single compilation.
When compiling a program written in C, the compiler goes through several steps to translate it into machine code that can be executed on your target architecture or platform.
In general, the compiler performs the following functions on your code:
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cc 語法
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cc 選項
實際上，您可以將數百個選項傳遞給編譯器，以微調程序的執行方式。
在這里，我們選擇了一些最有用且最常用的選項，您可能會需要這些選項來創建可執行文件。
-C
只需編譯代碼即可；不要嘗試鏈接源文件。
將創建目標文件，可以選擇稍后在一個單獨的步驟中鏈接目標文件以創建可執行文件。
-O [level]
創建優化的可執行文件。
編譯器將分析您的代碼，如果知道任何巧妙的技巧可以提高性能，它將在字節碼中實現它們。
該水平是一個可選的數字，字母或文字可以指定多少的優化應該做的。
例如，GNU編譯器集合允許選項-O0指定最小優化（默認值），
- O1和-O2指定中間優化級別，而-O3指定最大優化。
-Ofast可以用作-O3的別名，并且-Og將執行與調試器以后的分析兼容的優化。
優化需要更多的計算和內存，并且需要更長的時間才能完成。
x86系統的常見優化技巧包括減小指令大小以減少執行的計算量；
為值零實現專用寄存器（因為在大多數程序中通常使用零），
以及利用某些優勢來優化某些乘法和數組索引縮放操作所述的LEA（“加載有效地址”）指令。
-Wall
編譯時啟用“所有”（除了最深奧的）警告。
這是經常使用的好選擇，因為它可以提示您可能不是錯誤的任何情況，
但是您可能希望在編譯之前解決這些情況。
-ansi
禁用cc提供的大多數（但不是全部）非ANSI C兼容功能。
要遵守嚴格的ANSI標準，請啟用此選項。
這樣做將確保您的代碼具有完全可移植性，可以在任何其他系統上進行編譯。
-G
創建已編譯的可執行文件的調試版本。
編譯器將在編譯的可執行文件中包含有關哪個源文件的哪一行對應于哪個函數調用的信息。
當您逐步執行程序時，調試器以后可以使用此信息來顯示源代碼。
請注意，這將創建一個更大的可執行文件。
-D -ansi
通過將指定的值分配給符號名稱來定義編譯時的宏。
運行C預處理程序時，它將把name的任何實例擴展為value的文本。
-Idir
搜索目錄所包含的文件，其名稱以斜線（不要開始/）之前搜索照常目錄。
按照指定的順序搜索多個-I選項的目錄。
預處理程序首先在包含源文件的目錄中搜索#include文件，然后在以-I選項命名的目錄（如果有）中搜索/ usr / ucbinclude，然后在/ usr / include中搜索。
-Ldir
將dir添加到編譯器將在其中查找鏈接庫的目錄列表。
此選項傳遞給ld和/ usr / lib。
-llibrary
如果鏈接，則此選項將指示的庫添加到要鏈接的庫列表中。
例如，如果您使用的是C數學庫（libm）中的函數，則可以在編譯時使用-lm選項將其鏈接。
請注意您的庫的相互依賴關系，并確保在命令行上以正確的順序鏈接它們；
首先指定其他庫將依賴的任何庫。
例如，“ -lGL -lGLU ”將首先搜索libGL，然后搜索libGLU。
libGLU依賴于libGL，因此，如果您顛倒了這些-l選項的順序，該程序將無法編譯。
-M
如果鏈接，請創建一個與輸出可執行文件具有相同基本名稱的映射文件，但后綴為.map。
該映射文件包含符號列表及其地址。
-mmodel
指定編譯器和鏈接器使用的內存模型。
model的值包括s代表“小”存儲模型，m代表“中”，l代表“大”，f代表“ flat”（32位），c代表“ compact”，h代表“ huge”。
除非您確定需要此選項，否則可以忽略它。
-o file name
編譯后的可執行文件的輸出名稱。
如果未指定文件名，則編譯后的可執行文件將被命名為a.out。
-S
產生匯編程序源代碼，但在實際匯編之前停止。
-Uname
“取消定義”任何先前定義的名為name的宏，無論是在源代碼中還是在命令行中使用-D指定。
There are literally hundreds of options you can pass to the compiler to fine-tune how your program executes. Here we have selected some of the most useful and commonly-used options which you may need to create an executable file.
Be aware of your libraries' inter-dependencies and make sure to link them in the correct order on the command line; specify first any libraries which other libraries will depend on. For instance, "-lGL -lGLU" will search libGL first and then libGLU. libGLU depends on libGL, so if you reversed the order of these -l options, the program would not compile.
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cc 環境變量
以下環境變量會影響編譯過程：
LANG
LC_CTYPE
LC_MESSAGES
LC_ALL
這些環境變量控制編譯器使用本地化信息與不同的國家慣例一起工作的方式。
對于以UTF-8 編碼的英語，通用值為“ en_GB.UTF-8 ” 。
如果設置，LC_ALL變量將覆蓋所有其他語言環境設置。
要查看您當前的語言環境設置，請使用locale命令。
TMPDIR
如果設置了TMPDIR，它將指定用于臨時文件的目錄。
編譯器使用臨時文件保存一個編譯階段的輸出，該輸出將用作下一階段的輸入。
例如，預處理程序的輸出（即實際編譯器的輸入）在編譯過程中存儲在臨時文件中。
COMPILER_PATH
用冒號分隔的目錄列表，非常類似于PATH變量。
如果編譯器使用GCC_EXEC_PREFIX的值找不到子程序，則會在此目錄列表中搜索子程序。
LIBRARY_PATH
用冒號分隔的目錄列表，類似于PATH。
鏈接時，編譯器將在此目錄列表中搜索鏈接的庫，并使用GCC_EXEC_PREFIX的值找不到特殊的鏈接器文件。
CPATH
C_INCLUDE_PATH
CPLUS_INCLUDE_PATH
OBJC_INCLUDE_PATH
這些變量中的每一個都可能包含由特殊字符分隔的目錄列表，就像PATH一樣，編譯器將在其中查找頭文件。
特殊字符PATH_SEPARATOR取決于目標，并在構建時確定。對于大多數Linux目標，PATH_SEPARATOR是冒號。
CPATH指定要搜索仿佛用指定的目錄列表-I選項，但給定任何路徑后-I選項。
C_INCLUDE_PATH，CPLUS_INCLUDE_PATH和OBJC_INCLUDE_PATH僅在預處理指定的特定語言時適用。
每個命令都指定要搜索的目錄列表，就像使用-isystem指定的一樣，但是在命令行上使用-isystem選項指定的任何路徑之后。
在所有這些變量中，一個空元素指示編譯器搜索其當前工作目錄。
空元素可以出現在路徑的開頭或結尾。例如，如果CPATH的值為：/ special / include，則其效果與“ -I。-I / special / include ”相同。
DEPENDENCIES_OUTPUT
如果設置了此變量，則其值指定如何基于編譯器處理的非系統頭文件輸出make的依賴項。
系統頭文件在依賴項輸出中被忽略。
DEPENDENCIES_OUTPUT的值可以只是一個文件名，在這種情況下，將Make規則寫入該文件，
并從源文件名中猜測目標名稱。
或者該值可以采用“ file target ” 的形式，在這種情況下，使用target作為目標名稱將規則寫入文件file。
The following environment variables affect the compilation process:
LANG
LC_CTYPE
LC_MESSAGES
LC_ALL
These environment variables control the way the compiler uses localization information to work with different national conventions. A common value is "en_GB.UTF-8" for English language encoded in UTF-8. If set, the LC_ALL variable overrides all other locale settings.
To view your current locale settings, use the locale command.
TMPDIR
If TMPDIR is set, it specifies the directory to use for temporary files. The compiler uses temp files to hold the output of one stage of compilation that is to be used as input to the next stage. For example, the output of the preprocessor, which is the input to the actual compiler, is stored in a temporary file during the compilation process.
COMPILER_PATH
A colon-separated list of directories, much like the PATH variable. The compiler will search this list of directories for subprograms if it can't find them using the value of GCC_EXEC_PREFIX.
LIBRARY_PATH
A colon-separated list of directories, much like PATH. When linking, the compiler will search this list of directories for linked libraries, and for special linker files it can't find using the value of GCC_EXEC_PREFIX.
CPATH
C_INCLUDE_PATH
CPLUS_INCLUDE_PATH
OBJC_INCLUDE_PATH
Each of these variables may hold a list of directories separated by a special character, much like PATH, in which the compiler will look for header files. The special character, PATH_SEPARATOR, is target-dependent and determined at build time. For most Linux targets, PATH_SEPARATOR is a colon.
CPATH specifies a list of directories to be searched as if specified with the -I option, but after any paths given with the -I option.
C_INCLUDE_PATH, CPLUS_INCLUDE_PATH, and OBJC_INCLUDE_PATH apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with -isystem, but after any paths given with -isystem options on the command line.
In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the value of CPATH is :/special/include, that has the same effect as "-I. -I/special/include".
DEPENDENCIES_OUTPUT
If this variable is set, its value specifies how to output dependencies for make based on the non-system header files processed by the compiler. System header files are ignored in the dependency output.
The value of DEPENDENCIES_OUTPUT can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form "file target", in which case the rules are written to file file using target as the target name.
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cc 示例
編譯文件myfile.c。輸出將被寫入可執行文件a.out。
編譯文件myfile.c并將其命名為已編譯的可執行輸出文件myexe。
編譯文件myfile.c并將已編譯的可執行文件輸出為myexe，如果發生則在編譯期間顯示警告。
編譯myfile.c文件的可執行myexe，連接的libx11庫和編譯過程中發出任何警告適用。
編譯myfile.c文件的可執行myexe，連接的libx11庫，嚴格遵守ANSI C標準，如果適用發出警告。
Compile the file myfile.c. Output will be written to the executable file a.out.
Compile the file myfile.c and name the compiled executable output file myexe.
Compile the file myfile.c and output the compiled executable as myexe, displaying warnings during compilation if they occur.
Compile myfile.c to the executable myexe, linking the libX11 library and issuing any applicable warnings during compilation.
Compile myfile.c to the executable myexe, linking the libX11 library, adhering strictly to ANSI C standards, and issuing warnings if applicable.
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其他命令行
cut | cu | csplit | crontab | cpio | continue | compress | col | cmp | cksum | chsh | chroot | chkey | cd | chmod | cp | comm | chown | cal | calendar | clear | chfn | cancel | cat | cfdisk | checkeq | checknr | chgrp |