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C++: Add a 'good' example as well.

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This commit is contained in:
Geoffrey White
2024-07-08 11:06:21 +01:00
parent d52210d565
commit 4f0d725acd
4 changed files with 20 additions and 14 deletions
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5
cpp/ql/src/Likely Bugs/Memory Management/ReturnStackAllocatedMemory.cpp
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@@ -1,5 +0,0 @@
Record *mkRecord(int value) {
Record myRecord(value);
return &myRecord; // BAD: return a pointer to `myRecord`, which is a stack-allocated object
}

19
cpp/ql/src/Likely Bugs/Memory Management/ReturnStackAllocatedMemory.qhelp
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@@ -5,22 +5,23 @@
<overview>
<p>This rule finds return statements that return pointers to an object allocated on the stack.
The lifetime of a stack allocated memory location only lasts until the function returns, and
the contents of that memory become undefined after that. Clearly, using a pointer to stack
<p>This rule finds return statements that return pointers to an object allocated on the stack.
The lifetime of a stack allocated memory location only lasts until the function returns, and
the contents of that memory become undefined after that. Clearly, using a pointer to stack
memory after the function has already returned will have undefined results. </p>
</overview>
<recommendation>
<p>Use the functions of the <tt>malloc</tt> family to dynamically allocate memory on the heap for data that is used across function calls.</p>
<p>Use the functions of the <tt>malloc</tt> family, or <tt>new</tt>, to dynamically allocate memory on the heap for data that is used across function calls.</p>
</recommendation>
<example><sample src="ReturnStackAllocatedMemory.cpp" />
<example>
<p>The following example allocates an object on the stack and returns a pointer to it. This is incorrect because the object is deallocated
when the function returns, and the pointer becomes invalid.</p>
<sample src="ReturnStackAllocatedMemoryBad.cpp" />
<p>To fix this, allocate the object on the heap using <tt>new</tt> and return a pointer to the heap-allocated object.</p>
<sample src="ReturnStackAllocatedMemoryGood.cpp" />
</example>
<references>

5
cpp/ql/src/Likely Bugs/Memory Management/ReturnStackAllocatedMemoryBad.cpp Normal file
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@@ -0,0 +1,5 @@
Record *mkRecord(int value) {
Record myRecord(value);
return &myRecord; // BAD: returns a pointer to `myRecord`, which is a stack-allocated object.
}

5
cpp/ql/src/Likely Bugs/Memory Management/ReturnStackAllocatedMemoryGood.cpp Normal file
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@@ -0,0 +1,5 @@
Record *mkRecord(int value) {
Record *myRecord = new Record(value);
return myRecord; // GOOD: returns a pointer to a `myRecord`, which is a heap-allocated object.
}