vcl methods + exceptions corrupt memory with bcc64 - 64-bit

Question

My colleagues and I had a strange bug in a C++ Builder program and boiled it down to the following snippet:
#include <vcl.h>
#include <iostream>
void SIDE_EFFECTS() {
if (StrToFloat("1337")) {
throw "abc";
}
}
int _tmain(int argc, _TCHAR* argv[])
{
double innocent = StrToFloat("42");
std::cout << innocent << std::endl;
try {
SIDE_EFFECTS();
} catch (...) {
}
std::cout << innocent << std::endl;
return 0;
}
Expected Output:
42
42
Actual Output when compiled for 64bit/ReleaseBuild/OptimizationsON:
42
1337
Compiler (latest 10.1 Berlin version of C++ Builder):
Embarcadero C++ 7.20 for Win64 Copyright (c) 2012-2016 Embarcadero Technologies, Inc.
Embarcadero Technologies Inc. bcc64 version 3.3.1 (35759.1709ea1.58602a0) (based on LLVM 3.3.1)
The internet says [citation needed] that the bug is always in the user program but never in the compiler or standard library, so please enlighten us if/where we do things that are not to be done in C++ / C++ Builder.

Answer 1

Strictly speaking, there is nothing wrong with this code, so it has to be a compiler bug. File a bug report at Quality Portal.
That being said, you should generally stay away from using catch (...). If you are going to catch an exception at all, at least catch what you are expecting and willing to handle:
catch (const char *)
Let anything unexpected pass through and be handled higher up the caller chain.
I would not recommend throwing a string literal directly. It is better to wrap it in a std::runtime_error or System::Sysutils::Exception based object instead.
#include <vcl.h>
#include <iostream>
#include <stdexcept>
void SIDE_EFFECTS() {
if (StrToFloat("1337")) {
throw std::runtime_error("abc");
}
}
int _tmain(int argc, _TCHAR* argv[])
{
double innocent = StrToFloat("42");
std::cout << innocent << std::endl;
try {
SIDE_EFFECTS();
} catch (const std::runtime_error &) {
}
std::cout << innocent << std::endl;
return 0;
}
#include <vcl.h>
#include <iostream>
void SIDE_EFFECTS() {
if (StrToFloat("1337")) {
throw Exception("abc");
}
}
int _tmain(int argc, _TCHAR* argv[])
{
double innocent = StrToFloat("42");
std::cout << innocent << std::endl;
try {
SIDE_EFFECTS();
} catch (const Exception &) {
}
std::cout << innocent << std::endl;
return 0;
}