关于makefile的问题:"CFLAGS"和"SHVER"? [英] Questions on makefile: "CFLAGS" and "SHVER"?

问题描述

在一个makefile文件中，我发现作者说

In a makefile, I found the author stated that

CFLAGS = -Wall -Wconversion -O3 -fPIC
SHVER = 2

这两行的功能是什么?

这是完整的makefile:

Here is the makefile in full:

CXX ?= g++
CFLAGS = -Wall -Wconversion -O3 -fPIC
SHVER = 2

all: svm-train svm-predict svm-scale

lib: svm.o
    $(CXX) -shared -dynamiclib svm.o -o libsvm.so.$(SHVER)

svm-predict: svm-predict.c svm.o
    $(CXX) $(CFLAGS) svm-predict.c svm.o -o svm-predict -lm
svm-train: svm-train.c svm.o
    $(CXX) $(CFLAGS) svm-train.c svm.o -o svm-train -lm
svm-scale: svm-scale.c
    $(CXX) $(CFLAGS) svm-scale.c -o svm-scale
svm.o: svm.cpp svm.h
    $(CXX) $(CFLAGS) -c svm.cpp
clean:
    rm -f *~ svm.o svm-train svm-predict svm-scale libsvm.so.$(SHVER)

推荐答案

这些只是makefile变量. CFLAGS是常用变量，其中包含将传递给C编译器的标志(例如gcc). Makefile变量稍后会扩展，因此当您看到例如

These are just makefile variables. CFLAGS is a commonly used variable which contains flags that will be passed to the C compiler (e.g. gcc). Makefile variables get expanded later, so when you see e.g.

svm.o: svm.cpp svm.h
    $(CXX) $(CFLAGS) -c svm.cpp

这将扩展为:

g++ -Wall -Wconversion -O3 -fPIC -c svm.cpp

类似地，SHVER是共享库的版本号，因此对于这种依赖关系和构建命令:

Similarly SHVER is a shared library version number, so in the case of this dependency and build command:

lib: svm.o
    $(CXX) -shared -dynamiclib svm.o -o libsvm.so.$(SHVER)

这将扩展为:

g++ -shared -dynamiclib svm.o -o libsvm.so.2

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