Description
Variable length argument is a feature that allows a function to receive any number of arguments. There are situations where we want a function to handle variable number of arguments according to requirement.1) Sum of given numbers2) Minimum of given numbersand many more. Variable number of arguments are represented by three dotes (…)To portably implement variadic functions in the C programming language, the standard stdarg. h header file is used. The older varargs. h header has been deprecated in favor of stdarg. h Note that the function does not know the number of arguments or their types. The function expects that the types will be int, and that the number of arguments is passed in the first argument (this is a frequent usage but by no means enforced by the language or compiler). In some other cases, for example printf, the number and types of arguments are figured out from a format string. In both cases, this depends on the programmer to supply the correct information. If fewer arguments are passed in than the function believes, or the types of arguments are incorrect, this could cause it to read into invalid areas of memory and can lead to vulnerabilities like the format string attackstdarg. h declares a type, va list, and defines four macros: va start, va arg, va copy, and va end. Each invocation of va start and va copy must be matched by a corresponding invocation of va end. When working with variable arguments, a function normally declares a variable of type va list (ap in the example) that will be manipulated by the macrosva start takes two arguments, a va list object and a reference to the function's last parameter (the one before the ellipsis; the macro uses this to get its bearings). It initialises the va list object for use by va arg or va copy. The compiler will normally issue a warning if the reference is incorrect (e. g. a reference to a different parameter than the last one, or a reference to a wholly different object), but will not prevent compilation from completing normallyva arg takes two arguments, a va list object (previously initialised) and a type descriptor. It expands to the next variable argument, and has the specified type. Successive invocations of va arg allow processing each of the variable arguments in turn. Unspecified behavior occurs if the type is incorrect or there is no next variable argumentva end takes one argument, a va list object. It serves to clean up. If you wanted to, for instance, scan the variable arguments more than once, you would re-initialise your va list object by invoking va end and then va start again on itva copy takes two arguments, both of them va list objects. It clones the second (which must have been initialised) into the first. Going back to the scan the variable arguments more than once example, this could be achieved by invoking va start on a first va list, then using va copy to clone it into a second va list. After scanning the variable arguments a first time with va arg and the first va list (disposing of it with va end), you could scan the variable arguments a second time with va arg and the second va list. Don't forget to va end the clone va listThese questions will give you basic idea for Examination Preparation and/or interview on Variable Number of Arguments for C Programming. Please Note: These questions are only for practice and understanding level of knowledge only. It is not necessary that these questions may or may not appear for examinations and/or interview questionsIn this practice test, because of large amount of questions (around 26 questions) some of questions may have repeatedI had to put as 70% pass rate because there may also be wrong answers from my side.
