Editing Cyclone (programming language) (section)

===Dangling pointers and region analysis===
Consider the following code, in C:
<syntaxhighlight lang="C">
 char *itoa(int i)
 {
    char buf[20];
    sprintf(buf,"%d",i);
    return buf;
 }
</syntaxhighlight>
The function <code>itoa</code> allocates an array of chars <code>buf</code> on the stack and returns a pointer to the start of <code>buf</code>. However, the memory used on the stack for <code>buf</code> is deallocated when the function returns, so the returned value cannot be used safely outside of the function. While [[GNU Compiler Collection]] and other compilers will warn about such code, the following will typically compile without warnings:
<syntaxhighlight lang="C">
 char *itoa(int i)
 {
    char buf[20], *z;
    sprintf(buf,"%d",i);
    z = buf;
    return z;
 }
</syntaxhighlight>
GNU Compiler Collection can produce warnings for such code as a side-effect of option {{code|-O2}} or {{code|-O3}}, but there are no guarantees that all such errors will be detected.
Cyclone does regional analysis of each segment of code, preventing dangling pointers, such as the one returned from this version of <code>itoa</code>. All of the local variables in a given scope are considered to be part of the same region, separate from the heap or any other local region. Thus, when analyzing <code>itoa</code>, the Cyclone compiler would see that <code>z</code> is a pointer into the local stack, and would report an error.