GCC如何在内存中存储成员函数？

本文介绍了GCC如何在内存中存储成员函数？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 我想尽量减少我的类在内存中占用的大小（数据和指令）。我知道如何最小化数据大小，但我不太熟悉GCC如何放置成员函数。 它们存储在内存中，它们在class 解决方案为了内存中数据表示的目的，C ++ c>通常具有单个实例（假设single- 继承）vtable指针指向该vtable（这实际上是一些数据包装在文本段）。Virtual member functions are very often implemented thru virtual method table (or vtable); a class having some virtual member functions usually have instances with a single (assuming single-inheritance) vtable-pointer pointing to that vtable (which is practically some data packed in the text segment).When you are using multiple-inheritance things become more complex, objects might have several vtable pointers.So if you have a class (either a root class, or using single-inheritance), the consumption for virtual member functions is one vtable pointer per instance (plus the small space needed by the single vtable itself). It won't change (for each instance) if you have only one virtual member function (or destructor) or a thousand of them (what would change is the vtable itself). Each class has its own single vtable (unless it has no virtual member function), and each instance has generally one (for single-inheritance case) vtable pointer.The GCC compiler is free to organize the vtable as it wishes (and its order and layout is an implementation detail you should not care about); see also this. In practice (for single-inheritance) for most recent GCC versions, the vtable pointer is the first word of the object, and the vtable contain function pointers in the order of virtual method declaration, but you should not depend on such details.The GCC compiler is free to organize the functions in the code segment as it wishes, and it would actually reorder them (e.g. for optimizations). Last time I looked, it ordered them in reverse order. But you certainly should not depend on that order! BTW GCC can inline functions (even when not marked inline) and clone functions when optimizing. You could also compile and link with link-time optimizations (e.g. make CXX='g++ -flto -Os'), and you could ask for profile-guided optimizations (for GCC: -fprofile-generate, -fprofile-use, -fauto-profile etc...)You should not depend on how the compiler (and linker) is organizing function code or vtables. Leave the optimizations to the compiler (and such optimizations depend upon your target machine, your compiler flags, and the compiler version). You might also use function attributes to give hints to the GCC (or Clang/LLVM) compiler (e.g. __attribute__((cold)), __attribute__((noinline)) etc etc....)If you really need to know how functions are placed (which IMHO is very wrong), study the generated assembly code (e.g. using g++ -O -fverbose-asm -S) and be aware that it could vary with compiler versions!If you need on Linux and Posix systems at runtime to find out the address of a function from its name, consider using dlsym (for Linux, see dlsym(3), which also documents dladdr). Be aware of name mangling, which you can disable by declaring such functions as extern "C" (see C++ dlopen minihowto).BTW, you might compile and link with -rdynamic (which is very useful for dlopen etc...). If you really need to know the address of functions, use nm(1) as nm -C your-executable.You might also read the ABI specification and calling conventions for your target platform (and compiler), e.g. Linux x86-64 ABI spec. 这篇关于GCC如何在内存中存储成员函数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！