Variadic function (va_arg) doesn’t work with float?

by

Parameters of functions that correspond to ... are promoted before passing to your variadic function. char and short are promoted to int, float is promoted to double, etc.

6.5.2.2.7 The ellipsis notation in a function prototype declarator causes
argument type conversion to stop after the last declared parameter. The default argument
promotions are performed on trailing arguments.

The reason for this is that early versions of C did not have function prototypes; parameter types were declared at the function site but were not known at the call site. But different types are represented differently, and the representation of the passed argument must match the called function’s expectation. So that char and short values could be passed to functions with int parameters, or float values could be passed to functions with double parameters, the compiler “promoted” the smaller types to be of the larger type. This behavior is still seen when the type of the parameter is not known at the call site — namely, for variadic functions or functions declared without a prototype (e.g., int foo();).

More Related Contents:

  1. error: incompatible types for a function that returns float in C
  2. How do I restrict a float value to only two places after the decimal point in C?
  3. Passing variable number of arguments around
  4. Dividing 1/n always returns 0.0 [duplicate]
  5. How to represent FLOAT number in memory in C
  6. Why does printf() promote a float to a double?
  7. What operations and functions on +0.0 and -0.0 give different arithmetic results?
  8. Does printf(“%x”,1) invoke undefined behavior?
  9. Checking if float is an integer
  10. Representing integers in doubles
  11. What is the fastest way to convert float to int on x86
  12. Why does adding a small float to a large float just drop the small one?
  13. Is GCC mishandling a pointer to a va_list passed to a function?
  14. Comparing floating point numbers in C
  15. Comparing float and double in C
  16. Is it safe to assume floating point is represented using IEEE754 floats in C?
  17. Count number of digits after `.` in floating point numbers?
  18. Status of __STDC_IEC_559__ with modern C compilers
  19. Is there a tool to know whether a value has an exact binary representation as a floating point variable?
  20. problems in floating point comparison [duplicate]
  21. Is fmod() exact when y is an integer?
  22. Trouble with float on C [duplicate]
  23. When does underflow occur?
  24. Serialize double and float with C
  25. C printf using %d and %f
  26. Comparing float and double
  27. Can a conversion from double to int be written in portable C
  28. clang 14.0.0 floating point optimizations
  29. Conditional tests in primality by trial division
  30. How to produce a NaN float in c?

Leave a Comment