How to understand tcl's return

I wanted to get the number of parameters of a proc from tcl and didn't want it to be printed in tclsh, so I used return

When I execute the following statement in the c environment

string tclCmd = "info args " + tclProcName + ";return";
    Tcl_Eval(interp, tclCmd.c_str());
    string res = Tcl_GetStringResult(interp);

The result of the execution is not printed in tclsh, but at the same time it is not possible to get the correct value

So I tried to write it like this：

string tclCmd = "info args " + tclProcName;
    Tcl_Eval(interp, tclCmd.c_str());
    string res = Tcl_GetStringResult(interp);
    Tcl_Eval(interp, "return");

This works, but I don't understand why it doesn't print out immediately when Tcl_Eval is executed, and the return statement is still valid afterwards

The return command is not helpful at all there. It triggers an exception condition that comes out of Tcl_Eval as a return code of TCL_RETURN instead of TCL_OK (that is converted by the outer structure of a procedure, if that is relevant). Instead, you should call Tcl_ResetResult(interp); after you have finished with the return value (or have taken another reference to it) to put things back to how they were before your command implementation was invoked.