/* GCC command summary */
Supplement the knowledge of GCC to avoid being told by nature that the compilation principle is not good ..
Parameter description: The-O parameter is used to specify the name of the generated program.
GCC test. C will compile a program named A. Out.
GCC test. C-o Test compiles a program named test.
2.-l parameters and-l Parameters
Parameter description: The-l parameter is used to specify the database to be linked by the program. The-l parameter is followed by the database name. For example, if I want to link to the math database, its database name is M, its library file name is libm. so (generally
Directory), it is easy to see that the library name is removed from the header lib and tail. So of the library file name.
The libraries in/lib and/usr/local/lib can be directly linked using the-l parameter. However, if the library files are not stored in these three directories, but put it in other directories. If we only use the-l parameter, the link will still go wrong. The error message is probably "/usr/bin/ld: cannot find-LXXX ", that is, the link program LD cannot find libxxx in the three directories. so, then another parameter-l will be used. For example, the common X11 library is located in the/usr/x11r6/lib directory, we need to use the-L/usr/x11r6/lib-lx11 parameter during compilation. The-l parameter is followed by the Directory Name of the library file. For example, if we put libtest. So in the/AAA/BBB/CCC directory, the Link parameter is-L/AAA/BBB/CCC-ltest.
It is always troublesome to manually write the link parameters. Fortunately, many library sdks provide programs that generate the link parameters. The name is usually XXXX-config, which is usually stored in the/usr/bin directory. For example, the MySQL Link parameter Generation Program is mysql_config (note the underline, which is special). Run mysql_config -- libs:
-L/usr/lib/x86_64-linux-gnu -lmysqlclient -lpthread -lz -lm -lrt -ldl
These are the link parameters required by MySQL. It is easy to run the command automatically generated!
In addition to the -- libs parameter, XXX-config also has a parameter -- cflags used to generate the header file containing the directory, that is, the-I parameter. Execute mysql_config -- cflags:
-I/usr/include/mysql -DBIG_JOINS=1 -fno-strict-aliasing -g
This is the header file directory required by MySQL.
Now the question is how to use these output results. The most direct method is copy, paste, or copy, A better way is to add the 'xxxx-config -- Libs -- cflags 'in the compilation command line, for example, compile a MySQL program: GCC MySQL. c 'mysql _ config -- Libs -- cflags'
OK (I mentioned this in my blog a few days ago, ^ _ ^)
3.-include and-I Parameters
Parameter description:-include is used to contain header files, but generally the header files included are implemented using # include xxxxxx in the source code.-include is rarely used.
-The I parameter is used to specify the header file directory. Generally, the/usr/include directory does not need to be specified. GCC knows where to find it, however, if the header file is not in/usr/include, We need to specify it with the-I parameter. For example, if the header file is placed in the/myinclude directory, the-I/myinclude parameter must be added to the compile command line, if this parameter is not added, you will get a "XXXX. h: No such file or directory "error. -The relative path can be used for the I parameter. For example, if the header file is in the current directory, you can use-I. to specify it. The -- cflags parameter we mentioned above is used to generate the-I Parameter
Parameter description: This is a program optimization Parameter. Generally,-O2 is used to optimize the program, such as GCC test. c-O2, the optimized program is smaller than the one not optimized, and the execution speed may also be improved.
Parameter description: used to compile a dynamic library, such as gcc-shared test. C-o libtest. So.
6. Several related environment variables (required when cmake is used)
Pkg_config_path: Specifies the path of the PC file used by PKG-config. The default path is/usr/lib/pkgconf.
Ig: The PC file is a text file, and the extension is. PC. It defines the installation path, Libs parameters, and cflags parameters of the Development Kit.
Cc: used to specify the C Compiler
Cxx: used to specify the cxx Compiler
Libs: similar to the above-libs
Cflags: similar to the preceding -- cflags
CC, cxx, Libs, and cflags are not commonly used for manual compilation and are sometimes used for configure.
Environment variable setting method: Export env_name = xxxxxxxxxxxxxxxxx