C++ 缺少默认参数 - 编译器错误
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Missing default argument - compiler error
提问by cnicutar
void func ( string word = "hello", int b ) {
// some jobs
}
in another function
//calling
func ( "", 10 ) ;
When I have compiled it, compiler emits error ;
当我编译它时，编译器发出错误；
default argument missing for parameter
Howcan I fix it without changing anything, of course, such as not making "int b = 0" ? Moreover, I want use that function like func ( 10 ) or func ( "hi" ) ? Is my compiler not do its job, properly ?
我怎样才能在不改变任何东西的情况下修复它，当然，比如不制作 "int b = 0" ？此外，我想使用像 func ( 10 ) 或 func ( "hi" ) 这样的函数？ 我的编译器没有正确地完成它的工作吗？
回答by cnicutar
You can't have non-default parameters afteryour default parameters begin. Put another way, how would you specify a value for bleaving wordto the default of "hello" ?
默认参数开始后不能有非默认参数。换句话说，您将如何指定一个值以b保留word默认值 "hello" ？
回答by Chris
The arguments with a default value have to come in the end of the argument list.
具有默认值的参数必须出现在参数列表的末尾。
So just change your function declaration to
所以只需将您的函数声明更改为
void func(int b, string word = "hello")
回答by Mike Seymour
Parameters with default values have to come at the end of the list because, when calling the function, you can leave arguments off the end, but can't miss them out in the middle.
具有默认值的参数必须放在列表的末尾，因为在调用函数时，您可以将参数放在末尾，但不能在中间遗漏它们。
Since your arguments have different types, you can get the same effect using an overload:
由于您的参数具有不同的类型，您可以使用重载获得相同的效果：
void func ( string word, int b ) {
// some jobs
}
void func ( int b ) { func("hello", b); }
回答by iammilind
The error message is proper. If the default argument is assigned to a given parameter then all subsequent parameters should have a default argument. You can fix it in 2 ways;
错误信息是正确的。如果将默认参数分配给给定参数，则所有后续参数都应具有默认参数。您可以通过两种方式修复它；
(1) change the order of the argument:
(1) 改变参数的顺序：
void func (int b, string word = "hello");
(2) Assign a default value to b:
(2) 为 分配一个默认值b：
void func (string word = "hello", int b = 0);
回答by anatolyg
You cannot fix it without changing anything!
你不能在不改变任何东西的情况下修复它！
To fix it, you can use overloading:
要修复它，您可以使用重载：
void func ( string word, int b ) {
// some jobs
}
void func ( string word ) {
func( word, 999 );
}
void func ( int b ) {
func( "hello", b );
}
