Re: Question of compile C++ code with g++

[Bernd Strieder]

Hello,

Sen-Lung Chen wrote:

> g++: cannot specify -o with -c or -S and multiple compilations

The compiler driver g++ has two basic modes of operation: Producing
object files, and producing executables. There are more modes, but that
is beyond what you need now.

Producing object files is triggered by the -c option and requires a
source file to be compiled as argument and optionally an output
filename via -o.

Producing an executable, i.e. linking, is triggered by not specifying an
option changing the mode, i.e. not -c. You may specify source files,
object files, libraries to be compiled and linked, and there must be a
main function in one of these files, or linking fails.

So in your case there should be

g++ -c file.cc -o file.o

for every source file, and

g++ -o executablename object1.o object2.o main.o

to produce the executable.

There are abbreviations:

1.

g++ -c file1.cc file2.cc file3.cc

(note that there must not be a -o) is about the same as:

g++ -c file1.cc -o file1.o
g++ -c file2.cc -o file2.o
g++ -c file2.cc -o file3.o


2.

g++ -o executablename object1.cc object2.cc main.cc -lm

(note that there must be a main function somewhere) is about the same as

g++ -c object1.cc -o temporary1.o
g++ -c object2.cc -o temporary2.o
g++ -c main.cc -o temporary3.o
g++ -o executablename temporary[123].o -lm
rm temporary[123].o

So your problem was, that you were mixing abbreviations and the basic
invocations in ways that are not allowed.

Hope this helps,

Bernd Strieder