C++: Add test and placeholder query.

cpp/ql/src/Critical/MissingCheckScanf.ql

@@ -0,0 +1,14 @@
+/**
+ * @name TODO
+ * @description TODO
+ * @kind problem
+ * @problem.severity TODO
+ * @security-severity TODO
+ * @precision TODO
+ * @id cpp/missing-check-scanf
+ * @tags TODO
+ */
+
+import cpp
+
+select "TODO"

cpp/ql/test/query-tests/Critical/MissingCheckScanf/MissingCheckScanf.qlref

@@ -0,0 +1 @@
+Critical/MissingCheckScanf.ql

cpp/ql/test/query-tests/Critical/MissingCheckScanf/test.cpp

@@ -0,0 +1,195 @@
+typedef struct {} FILE;
+
+int scanf(const char *format, ...);
+int fscanf(FILE *stream, const char *format, ...);
+int sscanf(const char *s, const char *format, ...);
+
+void use(int i);
+
+void set_by_ref(int &i);
+void set_by_ptr(int *i);
+bool maybe();
+
+FILE *get_a_stream();
+const char *get_a_string();
+
+int main()
+{
+	// --- simple cases ---
+
+	{
+		int i;
+
+		scanf("%d", &i); // BAD: may not have written `i`
+		use(i);
+	}
+
+	{
+		int i;
+
+		if (scanf("%d", &i) == 1) // GOOD: checks return value
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i = 0;
+
+		scanf("%d", &i); // GOOD: we assume the initialization of `i` is a reasonable default
+		use(i);
+	}
+
+	// --- different scanf functions ---
+
+	{
+		int i;
+
+		fscanf(get_a_stream(), "%d", &i); // BAD: may not have written `i`
+		use(i);
+	}
+
+	{
+		int i;
+
+		sscanf(get_a_string(), "%d", &i); // BAD: may not have written `i`
+		use(i);
+	}
+
+	// --- different ways of checking ---
+
+	{
+		int i;
+
+		if (scanf("%d", &i) >= 1) // GOOD
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i;
+
+		if (scanf("%d", &i) == 1) // GOOD
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i;
+
+		if (scanf("%d", &i) != 0) // GOOD (just barely)
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i;
+
+		if (scanf("%d", &i) == 0) // BAD: checks return value incorrectly
+		{
+			use(i);
+		}
+	}
+
+	{
+		bool b;
+		int i;
+
+		b = scanf("%d", &i); // GOOD
+
+		if (b >= 1)
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i, j;
+
+		if (scanf("%d %d", &i) >= 2) // GOOD
+		{
+			use(i);
+			use(j);
+		}
+	}
+
+	{
+		int i, j;
+
+		if (scanf("%d %d", &i) >= 1) // BAD: checks return value incorrectly
+		{
+			use(i);
+			use(j);
+		}
+	}
+
+	// --- different initialization ---
+
+	{
+		int i;
+		i = 0;
+
+		scanf("%d", &i); // GOOD
+		use(i);
+	}
+
+	{
+		int i;
+
+		set_by_ref(i);
+		scanf("%d", &i); // GOOD: we have to assume `i` was initialized
+		use(i);
+	}
+
+	{
+		int i;
+
+		set_by_ptr(&i);
+		scanf("%d", &i); // GOOD: we have to assume `i` was initialized
+		use(i);
+	}
+
+	{
+		int i;
+
+		if (maybe())
+		{
+			i = 0;
+		}
+
+		scanf("%d", &i); // BAD: `i` may not have been initialized
+		use(i);
+	}
+
+	// --- weird formatting strings ---
+
+	{
+		int i;
+
+		if (scanf("%n %d", &i) >= 1) // GOOD (`%n` does not consume input)
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i;
+
+		if (scanf("%% %d", &i) >= 1) // GOOD (`%%` does not consume input)
+		{
+			use(i);
+		}
+	}
+
+	{
+		int i;
+
+		if (scanf("%*d %d", &i) >= 1) // GOOD (`%*d` does not consume input)
+		{
+			use(i);
+		}
+	}
+}