Compiler/CCSTUDIO: expression must have a constant value with function pointer

Erich Schroeter

Part Number: CCSTUDIO
Other Parts Discussed in Thread: TM4C1294NCPDT, SYSBIOS

Tool/software: TI C/C++ Compiler

The following code compiles successfully for me using MSVC, but I get the "#28 expression must have a constant value" error with the TI C++ compiler (C++14).

typedef void (*CallbackFunction)();

class Opt
{
public:
	constexpr Opt(const int val, const CallbackFunction & callback) :
		m_val(val),
		m_callback(callback)
	{ }

	const int m_val;
	const CallbackFunction & m_callback;
};

int g_value = 0;
void do_something()
{
	g_value++;
}

int main( void )
{
	constexpr const Opt opt1 = { 0, do_something };
}

Is there some compiler arg I can specify so that TI ARM compiler knows about function pointers at compile time? Or is this ability just not supported by ARM?

Invoking: ARM Compiler
"C:/ti/ccs1010/ccs/tools/compiler/ti-cgt-arm_20.2.1.LTS/bin/armcl" -mv7M4 --code_state=16 --float_support=FPv4SPD16 -me --include_path="C:/ti/tirtos_tivac_2_16_01_14/products/bios_6_45_02_31/packages/ti/sysbios/posix" --include_path="C:/ti/tirtos_tivac_2_16_01_14/products/TivaWare_C_Series-2.1.1.71b" --include_path="C:/ti/ccs1010/ccs/tools/compiler/ti-cgt-arm_20.2.1.LTS/include" --define=DEBUGSUP --define=ccs="ccs" --define=ccs --define=TIVAWARE --define=PART_TM4C1294NCPDT -g --c99 --relaxed_ansi --gcc --diag_suppress=10457 --diag_warning=225 --diag_warning=255 --diag_wrap=off --display_error_number --gen_func_subsections=on --abi=eabi --preproc_with_compile --preproc_dependency="main.d_raw" --include_path="C:/path/to/my/project/Debug/syscfg" --cmd_file="configPkg/compiler.opt" "../main.cpp"

over 5 years ago

0 George Mock over 5 years ago

TI__Guru**** 251230 points

I tried to build your code with several of the compilers available on the Compiler Explorer web site. For example, this is one attempt. Note that -std=c++14 is used. I never found a compiler that accepts it.

I'm not sure about the root cause of the problem. I'll get back to you on that.

Thanks and regards,

-George

0 Erich Schroeter over 5 years ago in reply to George Mock

Intellectual 410 points

I think I got it to work with a minor change.

Basically just created a CallbackFunction variable explicitly instead of assuming the function itself would work.

void _do_something()
{
    g_value++;
}
CallbackFunction do_something = &_do_something;

0 George Mock over 5 years ago in reply to Erich Schroeter

TI__Guru**** 251230 points

That looks like a reasonable solution.

Thanks and regards,

-George

Code Composer Studio™︎

Code Composer Studio forum

Compiler/CCSTUDIO: expression must have a constant value with function pointer