How to get argument names from clang::CallExpr?

Clang Frontend
1

Hi!

How can I retrieve the argument names from a clang::CallExpr? I was trying something along the following lines, but the dyn_cast returns null.

const auto *dr = clang::dyn_castclang::DeclRefExpr(expr->getArg(0));

auto name = dr->getDecl()->getName().str();

Thanks,

Kenth

2

What if you don't try to cast it to a `DeclRefExpr`, but you cast it to a `Expr` and `->dump()` it?

Note that some args are not represented by `DeclRefExpr` if they are literals such as IntegerLiteral or StringLiteral.

Also - are you sure you want argument names? In the code below, clang calls a1 and a2 arguments and p1 and p2 parameters:

void foo(int p1, int p2);

void bar()
{
    int a1 = 5;
    int a2 = 7;
    foo(a1, a2);
}

if you want parameters, you need to get the FunctionDecl from the callExpr and query its parameters to get their names.

Thanks,

Stephen.

3

What if you don't try to cast it to a `DeclRefExpr`, but you cast it
to
a `Expr` and `->dump()` it?

If I dump the CallExpr, I can see the following;

CallExpr 0x5640de2c08c8 'char *'

-ImplicitCastExpr 0x5640de2c08b0 'char *(*)(char *, const char *)' <FunctionToPointerDecay>
`-DeclRefExpr 0x5640de2c07f0 'char *(char *, const char *)' Function 0x5640de2916a8 'strcpy' 'char *(char *, const char *)'
-ImplicitCastExpr 0x5640de2c08f8 'char *' <LValueToRValue>
`-UnaryOperator 0x5640de2c0848 'char *' lvalue prefix '*' cannot overflow
  `-ImplicitCastExpr 0x5640de2c0830 'char **' <LValueToRValue>
    `-DeclRefExpr 0x5640de2c0810 'char **' lvalue ParmVar 0x5640de366998 'valueString' 'char **'

`-ImplicitCastExpr 0x5640de2c0928 'const char *' <NoOp>
  `-ImplicitCastExpr 0x5640de2c0910 'char *' <LValueToRValue>
    `-DeclRefExpr 0x5640de2c0860 'char *' lvalue Var 0x5640de366d88 'ptr1' 'char *'

I want to get the name of the first argument supplied to the call of
strcpy.

Note that some args are not represented by `DeclRefExpr` if they are

4

Can you show use the code corresponding to the CallExpr?

Also, when you say the “name of the first argument supplied…” that presumes that the first argument is always a variable. That’s not generally the case – any (well typed) argument will work. For example, your first argument in the dumped CallExpr above is pointer-dereference (I think *valueString?). So, you would, at the least, want your code to be

if (const auto *dr = clang::dyn_castclang::DeclRefExpr(expr->getArg(0))) {

auto name = dr->getDecl()->getName().str();

…

}

That said, you probably want expr->IgnoringImplicit(), since lvalues (e.g. variable names) are always implicitly cast to rvalues.

5

*valueString = (char*)malloc(len+1);
strcpy(*valueString, ptr1);