CCS/TM4C123GH6PM: Using "#define" with only one argument

shai kon

Expert 1960 points

Part Number: TM4C123GH6PM

Tool/software: Code Composer Studio

Hello,

The following code is copied from the TIVA C Launchpad workshop Lab 14:

#include "stdint.h"
#include "stdbool.h"
#include "inc/hw_memmap.h"
#include "inc/hw_ints.h"
#include "driverlib/debug.h"
#include "driverlib/gpio.h"
#include "driverlib/interrupt.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom.h"
#include "driverlib/sysctl.h"
#include "sensorlib/hw_isl29023.h"
#include "sensorlib/i2cm_drv.h"
#include "sensorlib/isl29023.h"
#define DEBUG

My question is about the last line (marked in red)
I've never seen #define used in such a way...I'm used to something as follows:
#define DEBUG some_number

Is this a typo ?

over 7 years ago

0 Charles Tsai over 7 years ago

TI__Guru**** 191316 points

Hi,

I think the reason is that the DEBUG is a predefined symbol. See below.

0 shai kon over 7 years ago in reply to Charles Tsai

Expert 1960 points

Thanks for the response.

Can you please explain the concept of a predefined symbol and how it works ?

0 Bob Crosby over 7 years ago in reply to shai kon

TI__Guru 72500 points

Defining a symbol without assigning it a value still allows it to be used in the following directive:

#if defined(DEBUG)
...
#endif

0 Charles Tsai over 7 years ago in reply to shai kon

TI__Guru**** 191316 points

If you look at the compiler command switches it is shown as below.

-mv7M4 --code_state=16 --float_support=FPv4SPD16 --abi=eabi -me --include_path="C:/ti/ccsv7/tools/compiler/ti-cgt-arm_16.9.4.LTS/include" --include_path="C:/ti/TivaWare_C_Series-2.1.4.178" -g --define=DEBUG --define=PART_TM4C123GH6PM --define=TARGET_IS_BLIZZARD_RB1 --display_error_number --diag_wrap=off --diag_warning=225

The --define is just like #define name in the C file. If the def is omitted then the name is set to 1. So DEBUG in this case is equal to 1. Below is the excerpt for the C TI ARM compiler user's guide.

0 shai kon over 7 years ago in reply to Bob Crosby

Expert 1960 points

I understand - Thanks.

And what about what Charles Tsai said ?
Does "DEBUG" have to be a predefined symbol for it to be used in the "if defined" directive ?

0 cb1_mobile over 7 years ago in reply to Charles Tsai

Guru 117855 points

May it be asked - 'Just where is the, 'Line to be drawn' - in awarding (only some) names - 'predefined status?'

Would it not (better) alert users to such "unique treatment" - via color coding (or other means) - rather than demanding a (more difficult & time consuming) search for - & studied review of, 'the compiler command switches?'

Neither (responding) vendor agent - in any way - created or abetted this issue - yet it proves, 'Less than Intuitive!' (and perhaps - unduly demanding.)

0 Bob Crosby over 7 years ago in reply to shai kon

TI__Guru 72500 points

No, it can be defined in the source file, but must be visible to the preprocessor before it is used.

#define DEBUG
...
#if defined(DEBUG)
....
#else
....
#endif

0 Charles Tsai over 7 years ago in reply to shai kon

TI__Guru**** 191316 points

For your reference.

Arm-based microcontrollers

Arm-based microcontrollers forum

CCS/TM4C123GH6PM: Using "#define" with only one argument