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<title>malloc function</title>
<head>
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<center>
<h1>malloc function </h1>
</center>
<hr>
<b>malloc</b> (memory allocation) is used to dynamically allocate memory
at run time. Possible uses for this function are:
<ul>
<li>Read records of an unknown length.
<li>Read an unknown number of database records.
<li><a href="../MISC/linklists.html">Link lists</a>.
</ul>
The simplest way to reserve memory is to code something like:
<p>
<table border=2 width=100% bgcolor=ivory>
<tr>
<td>
<pre>
main()
{
char string[1000];
<a href="strcpy.html">strcpy</a> (string, "Some text");
}
</pre>
</tr>
</td>
</table>
<p>
The example above has two problems:
<ul>
<li>If the data is less than
1000 bytes we are wasting memory.
<li>If the data is greater than 1000 bytes the program is going to crash.
<li>The 1000 bytes are reserved throught out the life of the program.
If this was a long running program that rarely used the memory, it would
again be wasteful.
</ul>
malloc allows us to allocate exactly the correct amount of memory and
with the use of <a href="free.html">free</a> only for the time it is required.
<p>
<hr>
<pre>
Library: stdlib.h
Prototype: void *malloc(size_t size);
Syntax: char * String;
String = (char *) malloc(1000);
</pre>
<hr>
<p>
Looking at the example syntax above, 1000 bytes are reserved and the pointer
<b>String</b> points to the first byte. The 1000 bytes are NOT initialized
by malloc. If the memory is NOT available, a
<a href="../SYNTAX/null.html">NULL</a> pointer is returned.
Please note, the cast <a href="../CONCEPT/cast.html">cast</a> is required to
return a pointer of the correct type.
<h2>Examples:</h2>
<img src="../../GRAPHICS/computer.gif"><a href="../EXAMPLES/linklst1.c"> example</a>
program.
<p>
<hr>
<h2>See Also:</h2>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../CONCEPT/data_types.html#char">char</a> data type.<p>
<img src=../../GRAPHICS/whiteball.gif>
<a href="free.html">free</a> function.<p>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../SYNTAX/sizeof.html">sizeof</a> operator.<p>
<hr>
<font color=brown>
<h2>C++</h2>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../../CPLUSPLUS/SYNTAX/new.html">new</a> is the C++ equivalent to malloc.<p>
<img src=../../GRAPHICS/whiteball.gif>
<a href="../../CPLUSPLUS/SYNTAX/delete.html">delete</a> is the C++ equivalent to
<a href="free.html">free</a>.<p>
</font>
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<p>
<hr>
<address>Martin Leslie
</address><p>
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