Does anyone know how to determine the data type of a variable at runtime?

I am trying to write some code that will convert the value of a variable
to string without knowing a priori its data type. The function will be passed
a pointer to the variable. How can this function determine the variable's
data type. The only thing I DO know is that this variable will never be
a structure or a union; it CAN be any numeric (including float and double) or
character (including string) type;

Please send e-mail and I will summarize to the net.

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There's no built-in way in C to do this, so you'll have to implement
it yourself.

One way to implement it would be to pass a second argument to the
function that accepts the pointer.  This argument should be an
indicator of the type (it should probably be an enum).

A variant would be to pass a struct instead of the pointer, something
like:

struct {
  enum {type_int, type_char, ...} type;
  union {int, char, ...} *ptr;
  } argument;

Your routine can then contain
  switch (argument.type) {
    case type_int: ...
    case type_char: ...
    ...
  }

Barry Margolin
Thinking Machines Corp.

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