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重构使用stringstreams的我被赋予这样的代码:用的memcpy
class Record
{
private:
unsigned short size_of_buffer;
char* buffer;
public:
bool was_marked_as_deleted();
};
bool Record::was_marked_as_deleted(){
if (buffer == NULL)
return false;
stringstream stream;
stream.write(buffer,size_of_buffer);
stream.seekg(0,stream.beg);
unsigned short size_of_first_field = 0;
stream.read((char*)(&size_of_first_field) , sizeof(size_of_first_field));
if (size_of_first_field > 1)
return false;
char first_field = 1;
stream.read((char*)(&first_field) , sizeof(first_field));
if (first_field != MARK_DELETED)
return false;
return true;
}
上述功能是
- 非常低效的,这是因为
stream.write(buffer,size_of_buffer);
线的 - 不可读。
所以我想用memcpy
而不是stringstreams
来重构它。 这是我想出了:
bool Record::was_marked_as_deleted(){
if(buffer==NULL)
return false;
unsigned short size_of_first_field= 0;
memcpy(&size_of_first_field,buffer,sizeof(size_of_first_field));
if (size_of_first_field > 1)
return false;
char first_field = 1;
//This line produces valgrind error
//EDIT: fixed it with the following IF statement
if (size_of_buffer > sizeof(size_of_first_field))
memcpy(&first_field,buffer+sizeof(size_of_first_field),sizeof(first_field));
if (first_field != MARK_DELETED)
return false;
return true;
}
现在的问题是,我的程序运行正常,但是当我valgrind
运行它,我得到这个:
==17340== Invalid read of size 1
==17340== at 0x8059452: Record::was_marked_as_deleted() (Record.cpp:161)
==17340== Address 0x5af2832 is 0 bytes after a block of size 2 alloc'd
这是为什么?为什么我的程序在valgrind下失败,而不是正常执行?
为什么这么说stream.write是非常低效的?它甚至没有对输入进行任何检查。这是否被实时调用?或者是一个非常大的时间?如果不是这样,你可能不会注意到它的差别 – Pedrom
它被称为很多次。函数不会将'buffer'的内容复制到流中? –
就像memcpy一样,你不会看到区别。检查一下Obvlious队长说什么是我准备给你的答案。 – Pedrom