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| author | Tobias Klauser <tklauser@distanz.ch> | 2008-01-27 11:37:44 +0100 |
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| committer | Tobias Klauser <tklauser@xenon.tklauser.home> | 2008-01-27 11:37:44 +0100 |
| commit | 7e0f021a9aec35fd8e6725e87e3313b101d26f5e (patch) | |
| tree | b1cacc4b24393f517aeb4610e9e1021f954307a8 /reference/C/SYNTAX/functions.html | |
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| -rw-r--r-- | reference/C/SYNTAX/functions.html | 138 |
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diff --git a/reference/C/SYNTAX/functions.html b/reference/C/SYNTAX/functions.html new file mode 100644 index 0000000..1f14822 --- /dev/null +++ b/reference/C/SYNTAX/functions.html @@ -0,0 +1,138 @@ +<title>Functions and passing arguments.</title> +<head> +<script language="JavaScript"> +</script> +</head> +<body bgcolor="#ffffcc"> +<center> +<hr> +<h1>Functions and passing arguments.</h1> +<hr> +</center> +A function is a block of code that can be executed many times by other +functions or its self. +<ul> +<li><a href=#2.1>Function basics.</a> +<li><a href=#2.2>Declaration.</a> +<li><a href=#2.3>Definition.</a> +<li><a href=#2.4>Passing values.</a> +<li><a href=#2.5>Passing pointers.</a> +<li><a href=#2.6>Passing Arrays.</a> +<li><a href=#2.7>Variable number of parms</a> +<li><a href=#2.8>Function recurssion.</a> +<li><a href=#2.9>Returning values.</a> +<li><a href=#2.10>Returning pointers.</a> +<font color="brown"> +<li> C++ <a href="../../CPLUSPLUS/CONCEPT/reference_variable.html">Reference variables</a> +<li> C++ <a href="../../CPLUSPLUS/CONCEPT/fundefault.html">Default parameters.</a> +<li> C++ <a href="../../CPLUSPLUS/CONCEPT/funcoverload.html">Function Overloading.</a> +</font> +</ul> + +<hr> +<a name=2.1><h2>Function Basics.</h2> +You should already understand the concept of functions! If you don't, you +are a sad sad man....<p> +Might expand on this one day.<p> +P.S. main() is a function. + +<a name=2.2><h2>Declaration.</h2> +Just like variables, all functions have to be +<a href="../glossary.html#declaration">declared</a> before use. Here is an +example. +<pre> + int add( int, int); +</pre> +This statement declares a function called <b>add</b>, it has two integer +arguments and returns an integer. + +<a name=2.3><h2>Definition.</h2> +The <a href="../glossary.html#definition">definition</a> is the meat of the +function. Heres an <a href="../EXAMPLES/function.c">example.</a> + +<a name=2.4><h2>Passing values.</h2> +Passing values is known as <b>call by value.</b> You actually pass a copy +of the variable to the function. If the function modifies the copy, the original +remains unaltered. The previous example demonstarted <b>call by value</b> +<a name=2.5><h2>Passing pointers.</h2> +This is known as <b>call by reference</b> and is an area worth spending some +time on. We do not pass the data to the function, instead we pass a pointer +to the data. This means that if the function alters the data, the original +is altered.<p> +<dd><img src="../../GRAPHICS/whiteball.gif"> +<a href="../EXAMPLES/pointer_func.c"> Example of passing a pointer to a scalar.</a> +<p> + +<font color=brown> +C++ has a nice feature called +<a href="../../CPLUSPLUS/CONCEPT/reference_variable.html">reference variables</a> +which is a tider +approch to modifing the contents of a passed variable. +</font> + +<a name=2.6><h2>Passing Arrays.</h2> +<dd><img src="../../GRAPHICS/whiteball.gif"> +<a href="../EXAMPLES/pointer1_func.c"> Example of passing a pointer to an integer array.</a> +<dd><img src="../../GRAPHICS/whiteball.gif"> +<a href="../EXAMPLES/pointer2_func.c"> Example of passing a pointer to a two +dimensional integer array.</a> +<dd><img src="../../GRAPHICS/whiteball.gif"> +<a href="../EXAMPLES/pointer3_func.c"> Example of passing a pointer to a +character array.</a> +<dd><img src="../../GRAPHICS/whiteball.gif"> +<a href="../EXAMPLES/pointer4_func.c"> Example of passing a two dimensional +character array.</a> +<h2><a name=2.7>Variable number of parms (...)</a></h2> + +<dd><img src="../../GRAPHICS/whiteball.gif"> +<a href="../EXAMPLES/var_func.c"> Example of passing an unknown number +of variables to a function</a> + +<dd><img src="../../GRAPHICS/man.gif"> +<a href="../MAN/va_start.htm"> Man page for va_start, va_end etc</a> + +<a name=2.8><h2>Function recurssion.</h2> +<a name=2.9><h2>Returning values.</h2> + +Normally you would return an 'int', 'char', 'float', or 'double' using this +technic. The obvious time to return a value would be to return a completion +code. +<p> +Here is an <a href="../EXAMPLES/function.c">example</a> +<p> +The contents of 'c' are copied into 'i'. + +<a name=2.10><h2>Returning pointers.</h2> + +Returning values is OK for the data types above but not very practical for +'char *' or structures. For these data types passing pointers can be more +appropriate. When using these pointers it is important to understand the +'<a href="../CONCEPT/storage_class.html#static2">static</a>' storage class +otherwise you are going to get some unpredictable +results. + +<p> + +<hr> +<p> +<center> +<table border=2 width="80%" bgcolor="ivory"> +<tr align=center> +<td width="25%"> +<a href="../cref.html"> Top</a> +</td><td width="25%"> +<a href="../master_index.html"> Master Index</a> +</td><td width="25%"> +<a href="keywords.html"> Keywords</a> +</td><td width="25%"> +<a href="../FUNCTIONS/funcref.htm"> Functions</a> +</td> +</tr> +</table> +</center> +<p> +<hr> +<address>Martin Leslie +</address><p> +</body> +</html> |