C99

[1] It extends the previous version (C90) with new features for the language and the standard library, and helps implementations make better use of available computer hardware, such as IEEE 754-1985 floating-point arithmetic, and compiler technology.

The C standards committee decided that it was of more value for compilers to diagnose inadvertent omission of the type specifier than to silently process legacy code that relied on implicit int.

[2] On platforms with IEEE 754 floating point: FLT_EVAL_METHOD == 2 tends to limit the risk of rounding errors affecting numerically unstable expressions (see IEEE 754 design rationale) and is the designed default method for x87 hardware, but yields unintuitive behavior for the unwary user;[9] FLT_EVAL_METHOD == 1 was the default evaluation method originally used in K&R C, which promoted all floats to double in expressions; and FLT_EVAL_METHOD == 0 is also commonly used and specifies a strict "evaluate to type" of the operands.

The following annotated example C99 code for computing a continued fraction function demonstrates the main features: Footnotes: A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available.

Historically, Microsoft has been slow to implement new C features in their Visual C++ tools, instead focusing mainly on supporting developments in the C++ standards.

Much effort went into developing a memory model, in order to clarify sequence points and to support threaded programming.