# CmdStan 2.17.0 build process not detecting the compiler correctly

**URL:** <https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946>\
**Category:** CmdStan\
**Created:** [September 19, 2017, 5:01pm UTC](https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946 "2017-09-19T17:01:49Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![jjramsey](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/jjramsey/32/3319_2.png) [@jjramsey](https://discourse.mc-stan.org/u/jjramsey)\
**Post date:** [September 19, 2017, 5:01pm UTC](https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946/1 "2017-09-19T17:01:49Z")

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If I try to run `make build` on RHEL 6, I get the following errors:

```
clang++ -Wall -I . -isystem stan/lib/stan_math/lib/eigen_3.3.3 -isystem stan/lib/stan_math/lib/boost_1.64.0 -isystem stan/lib/stan_math/lib/cvodes_2.9.0/include -std=c++1y -DBOOST_RESULT_OF_USE_TR1 -DBOOST_NO_DECLTYPE -DBOOST_DISABLE_ASSERTS -DBOOST_PHOENIX_NO_VARIADIC_EXPRESSION -I src -I stan/src -isystem stan/lib/stan_math/ -DEIGEN_NO_DEBUG -DFUSION_MAX_VECTOR_SIZE=12 -stdlib=libc++ -Wno-unused-function -Wno-uninitialized -DNO_FPRINTF_OUTPUT -pipe -c -O3 -o bin/cmdstan/stanc.o src/cmdstan/stanc.cpp
make: clang++: Command not found
make: *** [bin/cmdstan/stanc.o] Error 127

```

The immediate reason for the error is obvious: I don’t have clang++. The problem is why the build process is even invoking clang++ in the first place.

It looks like the makefile setup is buggy. In the top level makefile, the variable `CC` is set to `g++`, but after that, the makefile includes the file `stan/lib/stan_math/make/default_compiler_options` which sets `CC` to `clang++`, making the original initialization of `CC` completely pointless. The file `stan/lib/stan_math/make/detect_cc` doesn’t seem to make much sense either. It apparently tries to detect the C++ compiler by looking for strings in the variable `CC`, but either the user has already set `CC`, in which case detection already falls on the user, or the “detection” just regurgitates the default. It’s not like there’s any attempt to see if a compiler executable is in some path or the like.

This is also not a one-time problem affecting the build. Any time I need to compile a Stan file, I’d need to do `make CC=my-compiler path/to/stan_file`.

(There’s also the questionable decision to set `CC` to be the name of a C++ compiler, even though `CC` is a variable often traditionally set to a _C_ compiler, especially on Linux clusters.)

In any case, compiler detection seems to be a mess. As a “chicken wire and duct tape” fix, I suggest removing the variables `CC`, `O`, `O_STANC`, and `AR` from `stan/lib/stan_math/make/default_compiler_options`. That way, at least if the end user sets those variables in the top-level makefile, they’ll actually do what it looks like they’re supposed to do.

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**Author:** ![bgoodri](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/bgoodri/32/4451_2.png) [@bgoodri](https://discourse.mc-stan.org/u/bgoodri)\
**Post date:** [September 19, 2017, 5:03pm UTC](https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946/3 "2017-09-19T17:03:23Z")

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> [@jjramsey](#):
>
> As a “chicken wire and duct tape” fix

You can also put

```no-highlight
CC=g++

```

into a file called `local` in the `make/` directory.

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<div class="post-metadata">

**Author:** ![jjramsey](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/jjramsey/32/3319_2.png) [@jjramsey](https://discourse.mc-stan.org/u/jjramsey)\
**Post date:** [September 19, 2017, 5:17pm UTC](https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946/5 "2017-09-19T17:17:59Z")

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But it still doesn’t make sense to have `CC`, etc. set in both the main makefile and in `stan/lib/stan_math/make/default_compiler_options`, since the variables set in the latter totally override the former. Also, it would help to have comments in the main makefile indicate that this is the intended use of `make/local`, e.g. something like this:

```
##
# Users should only need to set these three variables for use:
#
# - CC: The compiler to use. Expecting g++ or clang++.
# - O: Optimization level. Valid values are {0, 1, 2, 3}.
# - AR: archiver (must specify for cross-compiling)
#
# To override them, create a file "local" in the "make" 
# subdirectory. Do NOT edit this file directly. (see
# the CmdStan guide for details).
##
CC = g++
O = 3
O_STANC = 0
AR = ar
```

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<div class="post-metadata">

**Author:** ![jjramsey](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/jjramsey/32/3319_2.png) [@jjramsey](https://discourse.mc-stan.org/u/jjramsey)\
**Post date:** [September 19, 2017, 5:19pm UTC](https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946/6 "2017-09-19T17:19:43Z")

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ariddell:

> Is it because clang++ is hard-coded in stan\_math/make/default\_compiler\_options?

Yes.

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<div class="post-metadata">

**Author:** ![bgoodri](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/bgoodri/32/4451_2.png) [@bgoodri](https://discourse.mc-stan.org/u/bgoodri)\
**Post date:** [September 19, 2017, 5:20pm UTC](https://discourse.mc-stan.org/t/cmdstan-2-17-0-build-process-not-detecting-the-compiler-correctly/1946/7 "2017-09-19T17:20:01Z")

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> [@jjramsey](#):
>
> But it still doesn’t make sense

I am not disputing that. I think we messed up when trying to get the makefiles in shape for 2.17.