[英]In-class initialization of std::map
我有這段不能在g ++ - 4.9.1下編譯的C ++代碼片段(我使用了命令“g ++ -c --std = c ++ 11 map.cc”)
#include <map>
#include <cstdint>
class A {
std::map<uint8_t, uint8_t> b = std::map<uint8_t, uint8_t>();
};
編譯時出現以下錯誤:
map.cc:5:52: error: expected ‘;’ at end of member declaration
std::map<uint8_t, uint8_t> b = std::map<uint8_t, uint8_t>();
^
map.cc:5:52: error: declaration of ‘std::map<unsigned char, unsigned char> A::uint8_t’ [-fpermissive]
In file included from /usr/lib/gcc/x86_64-linux-gnu/4.9/include/stdint.h:9:0,
from /usr/include/c++/4.9/cstdint:41,
from /usr/include/c++/4.9/bits/char_traits.h:380,
from /usr/include/c++/4.9/string:40,
from /usr/include/c++/4.9/stdexcept:39,
from /usr/include/c++/4.9/array:38,
from /usr/include/c++/4.9/tuple:39,
from /usr/include/c++/4.9/bits/stl_map.h:63,
from /usr/include/c++/4.9/map:61,
from map.cc:1:
/usr/include/stdint.h:48:24: error: changes meaning of ‘uint8_t’ from ‘typedef unsigned char uint8_t’ [-fpermissive]
typedef unsigned char uint8_t;
^
map.cc:5:59: error: expected unqualified-id before ‘>’ token
std::map<uint8_t, uint8_t> b = std::map<uint8_t, uint8_t>();
^
map.cc:5:43: error: wrong number of template arguments (1, should be 4)
std::map<uint8_t, uint8_t> b = std::map<uint8_t, uint8_t>();
^
In file included from /usr/include/c++/4.9/map:61:0,
from map.cc:1:
/usr/include/c++/4.9/bits/stl_map.h:96:11: error: provided for ‘template<class _Key, class _Tp, class _Compare, class _Alloc> class std::map’
class map
^
但是,如果我用int替換uint8_t,它編譯得很好。
FWIW,如果您需要解決,以下工作:
class A {
typedef std::map<uint8_t, uint8_t> B;
B b = B();
};
g ++的問題要大得多,每當你使用模板作為類成員時,如果任何參數(第一個除外)是typedef或在另一個名稱空間中,你就不能使用成員初始化。
typedef int I;
template<typename T1, typename T2> struct A {};
struct B {
A<I,float> a1=A<I,float>(); // works!
A<float,I> a2=A<float,I>(); // does not compile!
// This is the same reason the map does not comile, as string is a typedef
};
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