C++ std::pair 和前向声明的问题
不幸的是，我的模板代码仍然存在问题：
在文件“utility”的第 49 行：
error C2440: 'Initializing': cannot convert from 'const int' to 'IntersectionData *'
error C2439: 'std::pair<_Ty1,_Ty2>::second': member could not be initialized
我怎样才能找出问题出在哪里？我使用“IntersectionData*”对的唯一地方是这里：
#include "MRMaterialMatth.h"
#include "IntersectionData.h"
using namespace std;
struct IShaderMatth {
virtual ~IShaderMatth() {}
vector<pair<MaterialMatth,IntersectionData*> > traceCols;
};
并且没有任何其他编译器错误
我如何才能追踪到这一点？
//编辑：实用程序不是我的代码。它必须来自std..第49行的代码如下所示：
template<class _Other1,
class _Other2>
pair(const pair<_Other1, _Other2>& _Right)
: first(_Right.first), second(_Right.second)
{ // construct from compatible pair
}
第49行是注释edit2的行
： 我改变tracecols 内容的唯一地方如下所示：
IntersectionData* iDataOut = NULL;
if(newIData_out!=NULL)
{
iDataOut = new IntersectionData(*iData);
}
traceCols->push_back(make_pair(MaterialMatth(),iDataOut));
和
if(traceCols){
traceCols->push_back(make_pair(MaterialMatth(), NULL));
}
是
if(traceCols)
{
(*traceCols)[traceCols->size()].second = new IntersectionData(*newIData);
}
NULL 问题吗？它是一个指针，所以我应该被允许创建一个带有 NULL 的对，不是吗？
Unfortunately I still got a problem with my templated code from here:
C++ fancy template code problem
on line 49 in the file 'utility':
error C2440: 'Initializing': cannot convert from 'const int' to 'IntersectionData *'
error C2439: 'std::pair<_Ty1,_Ty2>::second': member could not be initialized
how could i figure out where the problem is? the only place i use a pair with 'IntersectionData*' is here:
#include "MRMaterialMatth.h"
#include "IntersectionData.h"
using namespace std;
struct IShaderMatth {
virtual ~IShaderMatth() {}
vector<pair<MaterialMatth,IntersectionData*> > traceCols;
};
and there are not any other compiler errors
how can I track down this?
//edit: utility is not my code. it must be from std.. the code of line 49 looks like this:
template<class _Other1,
class _Other2>
pair(const pair<_Other1, _Other2>& _Right)
: first(_Right.first), second(_Right.second)
{ // construct from compatible pair
}
line 49 is the line of the comment
edit2:
the only places where i change something about the content of tracecols look like this:
IntersectionData* iDataOut = NULL;
if(newIData_out!=NULL)
{
iDataOut = new IntersectionData(*iData);
}
traceCols->push_back(make_pair(MaterialMatth(),iDataOut));
and
if(traceCols){
traceCols->push_back(make_pair(MaterialMatth(), NULL));
}
and
if(traceCols)
{
(*traceCols)[traceCols->size()].second = new IntersectionData(*newIData);
}
is NULL the problem? it's a pointer, so i should be allowed to create a pair with NULL, no??
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评论（4）
尝试在调用
make_pair()时将NULL显式转换为IntersectionData *。Try explicitly casting the
NULLtoIntersectionData *in your call tomake_pair().初始化其中一对时出现问题。
问问自己，“什么初始化它？”
答案是向量traceCols。
现在问，“我在traceCols 中的哪里创建元素？”
一旦你回答了这个问题，你就应该知道出了什么问题。
There is a problem initializing one of those pairs.
Ask yourself, "What initializes that?"
The answer is the vector traceCols.
Now ask, "Where am I creating elements in traceCols?"
Once you answer that, you should know what is going wrong.
注意行
(*traceCols)[traceCols->size()].second = new IntersectionData(*newIData)- 看起来这会超出向量的范围（因为最大的向量的索引是size() - 1)。我不确定是否是 NULL 导致的 - 所以请注释掉该行，然后亲自查看（或尝试戴夫的建议）！如果不起作用，请注释掉另一个。最终，您要么找到哪一行，并能够提出更具体的问题，要么这些都不是，您就会知道必须在其他地方搜索。当我看到所有这些愚蠢的编译器错误消息时，我就是这么做的。
Watch out for the line
(*traceCols)[traceCols->size()].second = new IntersectionData(*newIData)- it seems like that would go out of the vector's bounds (since the largest index of a vector issize() - 1).I'm not sure if the NULL is causing it - so comment out that line, and see for yourself (or try Dave's suggestion)! If it doesn't work, comment out another. Eventually, you'll either find what line, and be able to ask a more specific question, or it'll be none of those things, and you'll know you have to search somewhere else. That's what I do when I see all these silly compiler error messages.
看起来您在
pair的某处有一个作业。编译器正在尝试将其转换为您列出的声明，但如果没有显式强制转换，它无法从 int 转换为指针。It looks like you have an assignment somewhere from a
pair<MaterialMatth,int>. The compiler is trying to convert from that to the declaration you listed, but it can't convert from an int to a pointer without an explicit cast.