What was the most dangerous programming mistake you have made in C?

Question

I am an intermediate C programmer. If you have made any coding mistake that you came to know later that it was the most hazardous / harmful to the total application please share

Answer 1

Two things comes to mind. Ths first was a function in embedded C (MCU) i tried to have some restrictions on an timer value as a entered a function. so I wrote

if(55000 < my_var < 65000)

My ida was to check like this:

if( (55000

But this is the equivilant or the result

if( (55000

and the result ended up that the if test was always true.

The secound was a pointer mistake. (simplyfied presented here)

get_data(BYTE **dataptr)
{ 
  ubyte* data = malloc(10);
  ... code ...
  *dataptr = &data[1];
}

 main()
 {
   BYTE *data
   get_data(&data);
   free(data);
 }

Thus resulting in a loss of 1 byte of memory for each time the get_data() function was called