如何改動makefile來避免沒有改動過的.c文件重復編譯

qfmeal

我知道只有改動過源文件，make的時候才會重新編譯。

我現(xiàn)在的情況是：
1.所有源文件沒動過，時間戳沒有變，任何操作都沒有；
2.生成的中間文件和目標文件都在，沒動過；
3.我的makefile是把不同目錄生成的所有中間文件都移到同一個obj目錄，最后在鏈接生成目標文件；
$(CUR_OBJ_CPP):%.o:%.cpp
        $(CC) $(CFLAGS) -c $^ -o $(OBJ_OUTPUT)/$@

但是每次 make的時候，所有的文件都會編譯一遍，現(xiàn)在文件多了，每次編譯很慢，所以想問下大牛們，這個問題怎么解決。

tsh185

那就用  make -j     多核編譯

sxhlinux

檢查系統(tǒng)時間

windoze

回復 1# qfmeal

1. 
   
2. $(CUR_OBJ_CPP):$(OBJ_OUTPUT)/%.o:%.cpp
   
3.         $(CC) $(CFLAGS) -c $^ -o $@
   

復制代碼

bskay

makefile太弱了,要用scons

yjh777

1. 寫對target依賴

2. 用 ccache

yjh777

有一段時間 gcc 默認就是 ccache 的符號鏈接，剛看了一下 fedora 23 發(fā)現(xiàn)又變回去了. 需要自己設置一下

官網(wǎng)地址:
    https://ccache.samba.org/

Features

    Keeps statistics on hits/misses.
    Automatic cache size management.
    Can cache compilations that generate warnings.
    Easy installation.
    Low overhead.
    Optionally uses hard links where possible to avoid copies.

Limitations

    Only knows how to cache the compilation of a single C/C++/Objective-C/Objective-C++ file. Other types of compilations (multi-file compilation, linking, etc) will silently fall back to running the real compiler.
    Only works with GCC and compilers that behave similar enough.
    Some compiler flags are not supported. If such a flag is detected, ccache will silently fall back to running the real compiler.

Why bother?

If you ever run make clean; make, you can probably benefit from ccache. It is common for developers to do a clean build of a project for a whole host of reasons, and this throws away all the information from your previous compilations. By using ccache, recompilation goes much faster.

Another reason to use ccache is that the same cache is used for builds in different directories. If you have several versions or branches of a software stored in different directories, many of the object files in a build directory can probably be taken from the cache even if they were compiled for another version or branch.

A third scenario is using ccache to speed up clean builds performed by servers or build farms that regularly check that the code is buildable.

You can also share the cache between users, which can be very useful on shared compilation servers.


*Is it safe?*

Yes. The most important aspect of a compiler cache is to always produce exactly the same output that the real compiler would produce. This includes providing exactly the same object files and exactly the same compiler warnings that would be produced if you use the real compiler. The only way you should be able to tell that you are using ccache is the speed.

ccache has been coded very carefully to try to provide these guarantees. However, if you experience any bugs, please report them.