构造临时对象时不允许成员函数重新声明 [英] Member function redeclaration not allowed when constructing temporary object
问题描述
大家好，
我对此代码有一个奇怪的编译器行为：
----代码片段的开头 - -
类基地
{
public：
static unsigned int ClassId（）;
};
class Derived
{
public：
static unsigned int ClassId（）{return 2; };
};
班级考试
{
public：
测试（unsigned int p1）{};
};
int main（int argc，char * argv []）
{
//这个工作
测试a（Derived :: ClassId（））;
//这次崩溃
测试（Derived :: ClassId（））;
返回0;
}
----代码片段结尾----
行
Test（Derived :: ClassId（））;
使用gcc 3.3.5和Visual Studio 8进行编译。使用gcc我得到
以下错误消息：
test.cpp：在函数`int main（int，char **）''：
test.cpp ：24：错误：`Test Derived :: ClassId（）''的原型没有
匹配任何
类'衍生''
test.cpp：11：错误：候选者是：static unsigned int
派生:: ClassId（）
test.cpp：24：错误：`Test Derived ::班级号（） '和`static unsigned int
Derived :: ClassId（）''不能超载
test.cpp：24：错误：`Test Derived :: ClassId的原型（ ）''没有
匹配任何
类`Derived''
test.cpp：11：错误：候选者是：static unsigned int
派生:: ClassId（）
test.cpp：24：错误：`Test Derived :: ClassId（）''和`static unsigned int
派生:: ClassId（）''不能超载
test.cpp：24：错误：声明`Test Derived :: ClassId（）''
类
不是定义
那么为什么它以这种方式失败了一个临时对象呢？如果
编译器不能处理相当于非临时情况的情况吗？
您是否对此行为有任何提示？
谢谢和致以最好的问候
Marco
Marco Wedekind写道：大家好，
我对这段代码有一个奇怪的编译器行为：
----代码片段的开头----
班级基地
{
公开：
static unsigned int ClassId（）;
};
class Derived
{
public：
static unsigned int ClassId（）{return 2; };
};
上课测试
{
公开：
测试（unsigned int p1）{};
};
int main（int argc，char * argv []）
//
//测试a（Derived :: ClassId （））;
//崩溃
测试（Derived :: ClassId（））;
返回0;
}
----代码片段结束----
测试行（Derived :: ClassId（））;
test.cpp：在函数`int main（ int，char **）''：
test.cpp：24：错误：`Test Derived :: ClassId（）''的原型不匹配'Derived'类中的任何
'
test.cpp：11：错误：候选者是：static unsigned int
Derived :: ClassId（）
test.cpp：24：错误：`Test Derived :: ClassId（）' '和`static unsigned int
Derived :: ClassId（）''不能超载
test.cpp：24：错误：原型对于`Test Derived :: ClassId（）''没有匹配任何类别`Derived''
test.cpp：11：错误：候选者是：static unsigned int
Derived :: ClassId（）
test.cpp：24：错误：`Test Derived :: ClassId（）''和`static unsigned int
Derived :: ClassId（）''不能重载
test.cpp：24：错误：
类之外的`Test Derived :: ClassId（）'声明是不是定义
那么为什么它会失败用这样的临时对象？如果
编译器不能处理相当于非临时情况的情况吗？
您是否对此行为有任何提示？
谢谢和最好的问候
Marco
编译器将第二行解释为函数原型
而不是临时对象实例化（请注意它在错误消息中删除了
括号）。规则是，如果声明可以将
解释为原型，它将是。
干杯！ --M
您好，
感谢您的回复！
你对如何规避这个问题有什么建议
语法上？什么是最优雅的解决方案？
最好的问候
Marco
我还有一点不明白的是：为什么它会掉落
括号？如果编译器会保留它们，我看不到
行如何：
Test（Derived :: ClassId（））;
可以解释为函数原型...
祝你好运
Marco
Hello all,
I have a strange compiler behaviour with this code:
---- Begin of code snippet ----
class Base
{
public:
static unsigned int ClassId();
};
class Derived
{
public:
static unsigned int ClassId() { return 2; };
};
class Test
{
public:
Test(unsigned int p1) {};
};
int main(int argc, char * argv[])
{
// This works
Test a(Derived::ClassId());
// This crashes
Test(Derived::ClassId());
return 0;
}
---- End of code snippet ----
The line
Test(Derived::ClassId());
failes to compile with gcc 3.3.5 and Visual Studio 8. With gcc I get
the following error message:
test.cpp: In function `int main(int, char**)'':
test.cpp:24: error: prototype for `Test Derived::ClassId()'' does not
match any
in class `Derived''
test.cpp:11: error: candidate is: static unsigned int
Derived::ClassId()
test.cpp:24: error: `Test Derived::ClassId()'' and `static unsigned int
Derived::ClassId()'' cannot be overloaded
test.cpp:24: error: prototype for `Test Derived::ClassId()'' does not
match any
in class `Derived''
test.cpp:11: error: candidate is: static unsigned int
Derived::ClassId()
test.cpp:24: error: `Test Derived::ClassId()'' and `static unsigned int
Derived::ClassId()'' cannot be overloaded
test.cpp:24: error: declaration of `Test Derived::ClassId()'' outside of
class
is not definition
So why does it fail with a temporary object in such a way? Should the
compiler not handle this case equivalent to the "non-temporary case"?
Do you have any hints on this behaviour?
Thanks and best regards
Marco
Marco Wedekind wrote:Hello all,
I have a strange compiler behaviour with this code:
---- Begin of code snippet ----
class Base
{
public:
static unsigned int ClassId();
};
class Derived
{
public:
static unsigned int ClassId() { return 2; };
};
class Test
{
public:
Test(unsigned int p1) {};
};
int main(int argc, char * argv[])
{
// This works
Test a(Derived::ClassId());
// This crashes
Test(Derived::ClassId());
return 0;
}
---- End of code snippet ----
The line
Test(Derived::ClassId());
failes to compile with gcc 3.3.5 and Visual Studio 8. With gcc I get
the following error message:
test.cpp: In function `int main(int, char**)'':
test.cpp:24: error: prototype for `Test Derived::ClassId()'' does not
match any
in class `Derived''
test.cpp:11: error: candidate is: static unsigned int
Derived::ClassId()
test.cpp:24: error: `Test Derived::ClassId()'' and `static unsigned int
Derived::ClassId()'' cannot be overloaded
test.cpp:24: error: prototype for `Test Derived::ClassId()'' does not
match any
in class `Derived''
test.cpp:11: error: candidate is: static unsigned int
Derived::ClassId()
test.cpp:24: error: `Test Derived::ClassId()'' and `static unsigned int
Derived::ClassId()'' cannot be overloaded
test.cpp:24: error: declaration of `Test Derived::ClassId()'' outside of
class
is not definition
So why does it fail with a temporary object in such a way? Should the
compiler not handle this case equivalent to the "non-temporary case"?
Do you have any hints on this behaviour?
Thanks and best regards
Marco
The compiler is interpreting the second line as a function prototype
rather than a temporary object instantiation (note that it dropped the
parentheses in the error message). The rule is that if a statement can
be interpreted as a prototype, it will be.
Cheers! --M
Hello,
thanks for your reply!
Do you have any suggestion on how to circumvent this problem
syntactically? What would be the most elegant solution?
Best regards
Marco
One thing I still do not understand is: Why does it drop the
parentheses? If the compiler would keep them, I do not see how the
line:
Test(Derived::ClassId());
could be interpreted as a function prototype...
Best regards
Marco
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