Linux 我不明白为什么编译器给我这个代码错误
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I don't understand why compiler is giving me error with this code
提问by pythonic
I have the following C code, which looks very correct to me. However, the clang compiler (infact gcc or any other C compiler too) thinks otherwise.
我有以下 C 代码，在我看来非常正确。但是，clang 编译器（实际上是 gcc 或任何其他 C 编译器）不这么认为。
typedef struct
{
struct timeval td_start;
struct timeval td_end;
} Timer;
void startTimer( struct Timer* ptimer )
{
gettimeofday( &(ptimer->td_start), NULL );
}
void stopTimer( struct Timer* ptimer )
{
gettimeofday( &(ptimer->td_end), NULL );
}
The compiler gives the following waring & error messages. Any idea what is wrong here?
编译器给出以下警告和错误消息。知道这里有什么问题吗？
./timing.h:14:25: warning: declaration of 'struct Timer' will not be visible
outside of this function [-Wvisibility]
void startTimer( struct Timer* ptimer )
^
./timing.h:16:27: error: incomplete definition of type 'struct Timer'
gettimeofday( &(ptimer->td_start), NULL );
~~~~~~^
./timing.h:14:25: note: forward declaration of 'struct Timer'
void startTimer( struct Timer* ptimer )
^
./timing.h:19:24: warning: declaration of 'struct Timer' will not be visible
outside of this function [-Wvisibility]
void stopTimer( struct Timer* ptimer )
^
./timing.h:21:27: error: incomplete definition of type 'struct Timer'
gettimeofday( &(ptimer->td_end), NULL );
~~~~~~^
./timing.h:19:24: note: forward declaration of 'struct Timer'
void stopTimer( struct Timer* ptimer )
采纳答案by NPE
Remove the structkeyword (it's not needed since you've already typedefed the struct):
删除struct关键字（不需要，因为您已经typedef编辑了结构）：
void startTimer( Timer* ptimer )
{
...
void stopTimer( Timer* ptimer )
{
...
Alternatively, remove the typedef:
或者，删除typedef：
struct Timer
{
struct timeval td_start;
struct timeval td_end;
};
void startTimer( struct Timer* ptimer )
{
...
void stopTimer( struct Timer* ptimer )
{
...
For more information, see Why should we typedef a struct so often in C?
有关更多信息，请参阅为什么我们应该在 C 中如此频繁地对结构进行 typedef？
回答by Didier Trosset
Either you
要么你
struct Timer
{
struct timeval td_start;
struct timeval td_end;
};
void startTimer( struct Timer* ptimer )
{
gettimeofday( &(ptimer->td_start), NULL );
}
Or you
或者您
typedef struct
{
struct timeval td_start;
struct timeval td_end;
} Timer;
void startTimer( Timer* ptimer )
{
gettimeofday( &(ptimer->td_start), NULL );
}
But don't mixup.
但不要混淆。
回答by DGomez
You created a type called Timer, just delete the word struct before the function parameters, like this, for example:
你创建了一个叫 Timer 的类型，把函数参数前面的 struct 字去掉就行了，像这样，例如：
void startTimer( Timer* ptimer )
{
gettimeofday( &(ptimer->td_start), NULL );
}
回答by Bo Persson
The reasonfor the error is that, when you get here
错误的原因是，当你到达这里时
void startTimer( struct Timer* ptimer )
there is no struct Timerin scope (just a typedef for an anonymous struct). So the compiler believes you want to declare a newtype struct Timerand use a pointer to that as a parameter.
没有struct Timer范围（只是匿名结构的 typedef）。因此，编译器认为您要声明一个新类型struct Timer并使用指向该类型的指针作为参数。
Actually doing that would be less than useful, as the type would just be visible insidethe function. That would make it practically impossible to pass in a parameter from outsidethe function.
实际上这样做没有多大用处，因为类型只会在函数内部可见。这将使得从函数外部传入参数实际上是不可能的。
So the compiler says that, while possibly allowed by the language, this doesn't look like a good idea!
所以编译器说，虽然语言可能允许，但这看起来不是一个好主意！
