在MSVC中对void *执行指针算术时出错

问题描述

Error    1    error C2036: 'const void *' : unknown size    file.cpp     111

我不跟着。 GCC从不抱怨void *指针运算，即使在 -ansi -pedantic -Wall 。有什么问题？

I don't follow. GCC never complains about void * pointer arithmetic, even on -ansi -pedantic -Wall. What's the problem?

以下是代码 -

struct MyStruct {

    const void *buf;    // Pointer to buffer  
    const void *bufpos; // Pointer to current position in buffer

};

...

size_t    someSize_t, anotherSize_t;
MyStruct *myStruct = (MyStruct *) userdata;
...
  if ( (myStruct->bufpos + someSize_t) > 
       (myStruct->buf + anotherSize_t) ) { // Error on this line
     ...

推荐答案

void * 指针。对于编译器知道如何处理的事物，转换 oData-> bufpos 和 oData-> anotherConstVoidPtr 。因为你似乎在寻找尺寸，大概是字节，转换到 char * 应该工作：

You can't do pointer math on a void * pointer. Cast oData->bufpos and oData->anotherConstVoidPtr to something the compiler knows how to deal with. Since you seem to be looking for sizes, which are presumably in bytes, casting to char * should work:

if (((char *)oData->bufpos + someSize_t) ...

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