[SOLVED] Loop condition and #define

Issue

I have an bin data table, for sample purposes:

static const unsigned char test_bin[28800] = {0};

#define TEST_DATA_COLUMNS 2
#define TEST_DATA_ROWS (sizeof(test_bin)/sizeof(float)/TEST_DATA_COLUMNS);    
static const float (* test_data)[TEST_DATA_COLUMNS] = (const float (*)[TEST_DATA_COLUMNS]) test_bin;

This fails with error: expected expression before ';' token:

for(size_t i = 0; i < TEST_DATA_ROWS ; i++);

But this works

size_t nrows = TEST_DATA_ROWS;
for(size_t i = 0; i < nrows ; i++);

Why?

godbot for quick testing

Solution

The problem is the trailing semi-colon at the end of the define for TEST_DATA_ROWS

#define TEST_DATA_ROWS (sizeof(test_bin)/sizeof(float)/TEST_DATA_COLUMNS);
                                                                         ^

This means that the preprocessor generates the following for your loop

for(size_t i = 0; i < (sizeof(test_bin)/sizeof(float)/TEST_DATA_COLUMNS); ; i++)
                                                                        ^ ^

Removing the ; from the end of the define would fix things.

Answered By - simonc

Answer Checked By - Cary Denson (WPSolving Admin)