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| <h4 class="subsection">A.2.1 Why Variadic Functions are Used</h4> |
| |
| <p>Ordinary C functions take a fixed number of arguments. When you define |
| a function, you specify the data type for each argument. Every call to |
| the function should supply the expected number of arguments, with types |
| that can be converted to the specified ones. Thus, if the function |
| ‘<samp><span class="samp">foo</span></samp>’ is declared with <code>int foo (int, char *);</code> then you must |
| call it with two arguments, a number (any kind will do) and a string |
| pointer. |
| |
| <p>But some functions perform operations that can meaningfully accept an |
| unlimited number of arguments. |
| |
| <p>In some cases a function can handle any number of values by operating on |
| all of them as a block. For example, consider a function that allocates |
| a one-dimensional array with <code>malloc</code> to hold a specified set of |
| values. This operation makes sense for any number of values, as long as |
| the length of the array corresponds to that number. Without facilities |
| for variable arguments, you would have to define a separate function for |
| each possible array size. |
| |
| <p>The library function <code>printf</code> (see <a href="Formatted-Output.html#Formatted-Output">Formatted Output</a>) is an |
| example of another class of function where variable arguments are |
| useful. This function prints its arguments (which can vary in type as |
| well as number) under the control of a format template string. |
| |
| <p>These are good reasons to define a <dfn>variadic</dfn> function which can |
| handle as many arguments as the caller chooses to pass. |
| |
| <p>Some functions such as <code>open</code> take a fixed set of arguments, but |
| occasionally ignore the last few. Strict adherence to ISO C<!-- /@w --> requires |
| these functions to be defined as variadic; in practice, however, the GNU |
| C compiler and most other C compilers let you define such a function to |
| take a fixed set of arguments—the most it can ever use—and then only |
| <em>declare</em> the function as variadic (or not declare its arguments |
| at all!). |
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