MSVC SAL与C ++ 2a合同

Question

在MSVC中，有SAL功能 ，可用于描述参数，结果等，而且效果很好，便携性也不错，C ++ 2a契约功能似乎做同样的事情，有人可以给一些他们之间的差异？

Answer 1

There is no real overlap between SAL and contracts. SAL is about annotating parameters and return values for describing some aspects of how the function uses them. Contracts about about describing what the function requires of its parameters and what the caller can expect of the return value. These sound similar, but they are very different.

For example, SAL has notions of whether a parameter is an input, output, or in/out parameter. That is a matter of what the function does with the parameters. Contracts have no such notion because they don't care what the function does with the parameter.

Now there is some overlap. Sometimes, what a function expects and what a function does align. For example, if a function expects a pointer parameter to not be nullptr , you would apply an [[pre: param != nullptr]] contract to that function. However, the SAL notion of _In_ pointer parameter annotations covers the same general idea: if the function uses the parameter as a valid pointer to an object, then naturally it cannot be nullptr . So _In_ protects from that.

SAL is ultimately about describing how the function uses the data; contracts are about the function's interface with the calling code.

Also, SAL is extremely limited in what you can express. It has a few complex statements like "is a null-terminated string", but it has no foundation on which you can build your own. Contracts are C++ expressions, and they therefore can verify anything that a C++ expression can verify.