Designing Public vs Private APIs
When you design a C++ library, one of your most important tasks is to clearly separate the public API, the set of functions, classes, and types that users of your library interact with from the private implementation, which contains the internal logic and details that users should not depend on. This separation is crucial for several reasons. First, it makes your library safer and easier to use: users see only what they need, with less risk of misusing internal details. Second, it allows you to change or optimize the internal implementation without breaking code that depends on your library, as long as the public API remains stable. Third, it leads to better maintainability, since you can organize code so that internal changes are isolated and do not ripple out to users.
main.cpp
mathlib.cpp
mathlib.h
1234567891011// main.cpp #include <iostream> #include "mathlib.h" int main() { std::cout << "3 + 5 = " << mathlib::add(3, 5) << "\n"; std::cout << "3 * 5 = " << mathlib::multiply(3, 5) << "\n"; // The following line would fail to compile, since double_value is private: // std::cout << double_value(10) << "\n"; }
In C++, you typically expose your public API through header files (.h or .hpp), which declare the functions and classes that users can call. The actual implementation often lives in source files (.cpp), which are compiled into the library. You can also hide helper functions, private classes, or variables in these source files, making them invisible to library users. By carefully controlling what you include in your public headers, you create a clear boundary between your library's interface and its inner workings.
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When you design a C++ library, one of your most important tasks is to clearly separate the public API, the set of functions, classes, and types that users of your library interact with from the private implementation, which contains the internal logic and details that users should not depend on. This separation is crucial for several reasons. First, it makes your library safer and easier to use: users see only what they need, with less risk of misusing internal details. Second, it allows you to change or optimize the internal implementation without breaking code that depends on your library, as long as the public API remains stable. Third, it leads to better maintainability, since you can organize code so that internal changes are isolated and do not ripple out to users.
main.cpp
mathlib.cpp
mathlib.h
1234567891011// main.cpp #include <iostream> #include "mathlib.h" int main() { std::cout << "3 + 5 = " << mathlib::add(3, 5) << "\n"; std::cout << "3 * 5 = " << mathlib::multiply(3, 5) << "\n"; // The following line would fail to compile, since double_value is private: // std::cout << double_value(10) << "\n"; }
In C++, you typically expose your public API through header files (.h or .hpp), which declare the functions and classes that users can call. The actual implementation often lives in source files (.cpp), which are compiled into the library. You can also hide helper functions, private classes, or variables in these source files, making them invisible to library users. By carefully controlling what you include in your public headers, you create a clear boundary between your library's interface and its inner workings.
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