Closed github-learning-lab[bot] closed 3 years ago
memcpy
4_memcpy_definitions.ql
where
clause so that the query finds all definitions of functions named memcpy
instead.Congratulations, looks like the query you introduced in b338449560965f22c76a58ae2ea6b881d5ae28dc finds the correct results!
If you created a pull request, merge it.
Let's continue to the next step.
Step 4: Anatomy of a query
Now let's analyze what you have written. A CodeQL query has the following basic structure:
The
from
/where
/select
part is the query clause: it describes what we are trying to find in the source code.Let's look closer at the query we wrote in the previous step.
Show the query
```ql import cpp from Function f where f.getName() = "strlen" select f, "a function named strlen" ```Imports
At the top of the query is
import cpp
. This is an import statement . It brings into scope the standard CodeQL library that models C/C++ code, allowing us to use its features in our query. We'll use this library in every query, and in later steps we'll also use some more specialized libraries.Classes
In the
from
section, there is a declarationFunction f
. Here we declare a variable namedf
which has the typeFunction
.Function
is a class declared in the standard library (you can jump to the definition usingF12
). A class represents a collection of values, in this case the collection of all C/C++ functions in the source code.Predicates
Now look at the expression
f.getName()
in thewhere
section. Here we call the predicategetName
on the variablef
of typeFunction
. Predicates are the building blocks of a query: they express logical properties that we want to hold. Some predicates return results (likegetName
) , and some predicates do not (they just assert that a property must be true).So far your query finds all functions with the name
strlen
. It does this by asserting that the result off.getName()
is equal to the string"strlen"
.