extern

问题 I'm in the process of moving code written to be compiled for one chip onto another chip. One issue that's come up is a multitude of multiple definition errors. Some of which appear to be due to the linker for the first chip letting me be lazy with declaring variables extern when they are to be used across multiple source files. I didn't use extern at all previously (declare and define a variable in something.h, use it in something.cpp and other source files that included something.h) and it

问题 I'm in the process of moving code written to be compiled for one chip onto another chip. One issue that's come up is a multitude of multiple definition errors. Some of which appear to be due to the linker for the first chip letting me be lazy with declaring variables extern when they are to be used across multiple source files. I didn't use extern at all previously (declare and define a variable in something.h, use it in something.cpp and other source files that included something.h) and it

问题 I'm in the process of moving code written to be compiled for one chip onto another chip. One issue that's come up is a multitude of multiple definition errors. Some of which appear to be due to the linker for the first chip letting me be lazy with declaring variables extern when they are to be used across multiple source files. I didn't use extern at all previously (declare and define a variable in something.h, use it in something.cpp and other source files that included something.h) and it

问题 I read that the extern keyword is implicit in the context of functions, so unless you specify otherwise using the static keyword ( which if I'm not mistaken is basically a completely separate concept from the static that variables employ—they just share a keyword ), they are visible to all object files. This makes sense; having the declarations be implicitly external, while technically unnecessary when the declarations are in the same file as the definition, is useful because the programmer

问题 I read that the extern keyword is implicit in the context of functions, so unless you specify otherwise using the static keyword ( which if I'm not mistaken is basically a completely separate concept from the static that variables employ—they just share a keyword ), they are visible to all object files. This makes sense; having the declarations be implicitly external, while technically unnecessary when the declarations are in the same file as the definition, is useful because the programmer

问题 Say we have some external linkage using the extern keyword. I have (in class1.cpp): MyClass* myClassVar = NULL; The constructor initializes the above, and destructor deletes. Then in class2.cpp and class3.cpp there is: extern MyClass* myClassVar; These classes use myClassVar (doing the usual null checks etc). Would a Singleton be preferred? (I know globals are bad etc, and a Singleton is just syntax sugar). Is there an advantage to change the above code to the below? static Singleton&

问题 Say we have some external linkage using the extern keyword. I have (in class1.cpp): MyClass* myClassVar = NULL; The constructor initializes the above, and destructor deletes. Then in class2.cpp and class3.cpp there is: extern MyClass* myClassVar; These classes use myClassVar (doing the usual null checks etc). Would a Singleton be preferred? (I know globals are bad etc, and a Singleton is just syntax sugar). Is there an advantage to change the above code to the below? static Singleton&

问题 Im using a C++ DLL for my C# project, DLL has a class inside which is created and destroyed by outer functions such as: class myClass { int N; public: //some elements and some functions myClass(int n) { N=n; } }; __declspec(dllexport) myClass * builderF(int n) { return new myClass(n); } __declspec(dllexport) void destroyerF(myClass * c) { delete c; } and these are in extern "C" {} body. How does the compiler let me use C++ features is "C" space? Isnt it for only C code? This is tested and

问题 I have a problem that could be viewed as an extension of this question in which the user is having problems with external aliases not working. The variation I am experiencing is that the two projects output the same file name. The first (we'll call Legacy since it's the older version) contains classes which have been binary-serialized. The second ( Current ) is the next version of my domain. I'm trying to create a conversion library ( Compatibility ) which will map Legacy to Current for use

问题 From Here it seems that default argument are not supported by C. I have the following method in exported library: extern "C" { __declspec (dllexport) uintptr_t Method(int freq, int *pRetval, bool *support2MHz); } If i made last argument optional like this: extern "C" { __declspec (dllexport) uintptr_t Method(int freq, int *pRetval, bool *support2MHz = NULL); } My dll is still compiled. My question is why? Everyone says the default arguments are not supported in C code. I use C++ for MS 2015.