关于C++ Quantlib开发中两类预处理指令的技术疑问

Great question—these preprocessor directives are a common gotcha when working with mature C++ libraries like QuantLib on modern Microsoft Visual Studio compilers. Let’s break down your questions one by one:

1. Why do we need to add these two directives? #

Modern versions of the MSVC compiler enforce strict security checks for C and C++ standard library functions/APIs. It flags older, potentially unsafe functions (like C’s strcpy, scanf, or certain legacy STL iterator patterns) as deprecated, meaning it will throw compilation warnings (or even errors, depending on your project settings) to push you toward safer alternatives (e.g., strcpy_s, scanf_s).

The _CRT_SECURE_NO_DEPRECATE macro disables these warnings for C standard library functions, while _SCL_SECURE_NO_DEPRECATE does the same for C++ Standard Template Library (STL) APIs. Since QuantLib and its Boost dependencies still use some of these legacy interfaces for backward compatibility, adding these macros tells the compiler: "I’m aware of the security risks here, and I take responsibility for using these APIs—don’t block my compilation or flood me with warnings."

2. Is this a requirement from QuantLib or Boost? #

Neither library explicitly requires these macros. Instead, they’re a workaround to make QuantLib/Boost play nice with modern MSVC compilers. Both libraries are long-lived and maintain compatibility with older compilers, so their codebase includes patterns that trigger MSVC’s security warnings. If you were using a different compiler like GCC or Clang, you’d likely never need to add these macros—their default warning settings don’t flag these legacy APIs as aggressively.

3. Do I always need to add such directives when using other external libraries? #

Absolutely not. This only applies in specific scenarios:

• The library relies on legacy C/C++ standard library APIs that your compiler (mostly MSVC) marks as deprecated for security reasons.
• Your project’s compiler settings are set to treat warnings as errors (a common practice in production code), which would block compilation without these macros.

If you’re working with a newer library that’s been updated to use modern, compiler-approved safe APIs, you won’t need these directives at all. And as mentioned earlier, non-MSVC compilers rarely require this workaround.

内容的提问来源于stack exchange，提问作者Nick Ben