Va_start
va_start is a C and C++ macro that initializes a variable argument list for accessing a function’s variable arguments.
Modern C, Third Edition
va_start is a C standard-library macro that initializes a variable argument list for access by va_arg and related operations.
- How it is used
- Initializes a va_list so variadic arguments can be consumed directly or forwarded to formatted-output functions.
- How deep it goes
- Explains initialization, typed retrieval, forwarding, cleanup, and the C23 parameter change, but not va_list internals.
- Examples
- Uses a formatted-output wrapper that initializes va_list and forwards it to vfprintf or vsnprintf.
- What you can do after
- Build a variadic wrapper that initializes, forwards, and finishes a variable argument list using <stdarg.h>.
Modern C
va_start is a C standard library macro that initializes a va_list for accessing a function's variable arguments.
- How it is used
- Initializes a va_list before a variadic function reads or forwards its unnamed arguments.
- How deep it goes
- Explains the initialization operand and lifecycle, but defers representation details and argument type encoding.
- Examples
- Uses a double-summing variadic function and a debugging wrapper that forwards arguments to vfprintf.
- What you can do after
- Build it from scratch by initializing, consuming or forwarding, and then ending a va_list.
Related concepts
- variadic argumentsused by · A variadic function or parameter accepts a variable number of arguments, often collecting the supplied values into a sequence of a specified type.
- failure modecontrasts with · A failure mode is a distinct way in which a system, component, process, or operation can fail or produce an undesirable result.
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