(C) const

Keyword being an abbreviation of 'constant'. Use const whenever possible.

int main()
{
  const int x = 69;
  return 0;
}

In functions const can be used to indicate a 'read-only' from ?struct

typedef struct
{
  int mX;
} MyStruct;
/* Most common */
void transmogrify1(const MyStruct * pMyStruct)
{
  /* pMyStruct->mX = 12; Error: cannot modify where pMyStruct points to */
  pMyStruct = 0; /* Okay, won't do harm to pMyStruct */
}
/* Most uncommon */
void transmogrify2(MyStruct * const pMyStruct)
{
  pMyStruct->mX = 12; /* Okay, can modify where pMyStruct points to */
  /* pMyStruct = 0;      Error: cannot modify where pMyStruct points to */
}
/* Common */
void transmogrify3(const MyStruct * const pMyStruct)
{
  /* pMyStruct->mX = 12; Error: cannot modify where pMyStruct points to */
  /* pMyStruct = 0;      Error: cannot modify where pMyStruct points to */
}

To indicate that MyStruct is only read from, use transmogrify1 and transmogrify3. To save typing, many choose transmogrify1.

'const' links

last edited (November 11, 2006) by bilderbikkel, Number of views: 1678, Current Rev: 4 (Diff)

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