How to compile code from stdin?

Question

The code is quite simple :

test$ cat test.cpp

int main()
{
}

Is there a way to compile the code that is coming from a standard output?

I have tried this :

cat test.cpp | g++ -

and some variations, but none produced executable.

Just some clarifications. I have a program which preprocess a file, and produces another file which I want to compile. I thought about not creating this intermediate file, but to instead produce the object file directly.

Why are people so interested in compiling from standard input? Is it that hard to generate a file and compile that? — David Rodríguez - dribeas, Jul 30 '13 at 13:13
Well, you are `cat`-ing a file... so the middle man is there. If your intention was typing directly into the compiler, then chances are that for anything not absolutely trivial you will make a typo and will have to retype (I know, I have used `cat` as an editor a few times which is fine if you never mistype)... — David Rodríguez - dribeas, Jul 30 '13 at 13:20
Don't do that. If you generate C or C++ code, generate it in some temporary file (perhaps in a *tmpfs* filesystem like `/tmp/`), and fork a `gcc` or a `make` process to compile it. Read [my answer here](http://stackoverflow.com/a/17709877/841108) — Basile Starynkevitch, Jul 30 '13 at 13:21
@DavidRodríguez-dribeas No, ´cat´ is not there. I have something else. A program which parses a header, and creates some code, which needs to be compiled into an obj file. — BЈовић, Jul 30 '13 at 13:24
@BasileStarynkevitch Any specific reason not to do it? I do not really care for the speed of the compilation. — BЈовић, Jul 30 '13 at 13:36
Read [my answer here](http://stackoverflow.com/a/17709877/841108) which gives a lot of reasons for not doing it. — Basile Starynkevitch, Jul 30 '13 at 13:37
For my part, I just needed to check the presence of a header. So, not creating a file is simpler than creating it then remove it. My solution: ``` is_header_present() { header_name=$1 gcc -o /dev/null $CFLAGS -x c++ - < — shamox, Sep 13 '22 at 02:12

score 47 · Accepted Answer · edited Jul 12 '23 at 20:36

47

The compiler would have probably told you:

-E or -x required when input is from standard input

Try

cat test.cpp | g++ -x c++ -

edited Jul 12 '23 at 20:36

Sean Bright

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answered Jul 30 '13 at 13:08

devnull

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Yes, it told me, but it didn't tell to put c++ after. After adding c++ it works – BЈовић Jul 30 '13 at 13:16
3

@BЈовић In these cases, you are supposed to read the documentation of the particular compiler flag you will be using. `-x` is documented to require the language as its argument. – Jul 30 '13 at 13:29
3

@H2CO3 The error message is not helpful at all (if you do not provide the language). Also, the ´-´ has to be at the end. Try to find such details in g++ documentation – BЈовић Jul 30 '13 at 13:34
1

@devnull Please explain the need for that last `-`; it appears it can be omitted, yet is somehow necessary? – GooseDeveloper Sep 09 '21 at 17:16

score 2 · Answer 2 · answered Jul 30 '13 at 13:26

2

Did you try this ?

$ cat tst.cpp | g++ -x c++ -

I have just tried it under Cygwin and had no problem.

answered Jul 30 '13 at 13:26

Shlublu

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How to compile code from stdin?

2 Answers2

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