错误：调用'begin(long double [nPoints])'没有匹配函数;使用硬编码的 int 与整数变量初始化向量
error: no matching function for call to 'begin(long double [nPoints])' ; initializing vector with a hardcoded int versus an integer variable
我写了一个处理幻数的代码，现在我正在尝试将幻数放入变量中。 本质上，我创建一个具有固定数量的元素的数组，填充数组，然后将其转换为向量。 只要我将数组创建为：
long double yy[5];
vector<long double> YY;
YY.insert(YY.begin(), begin(yy), end(yy));
但是如果我将数组创建为：
int nPoints = 5;
long double yy[nPoints];
vector<long double> YY;
YY.insert(YY.begin(), begin(yy), end(yy));
我尝试将nPoints转换为其他数据类型，检查以确保它是我分配的数据类型等，但我没有任何运气。
// non functional code
#include <iostream>
#include <vector>
using namespace std;
int main(){
int nPoints = 5;
// initialize an input vector
vector<long double> xx = {1, 2, 3, 4, 5};
// compute some function of xx in a loop
long double yy[nPoints];
for(int i = 0; i<=nPoints - 1; i++){
yy[i] = 2*xx[i];
}
// convert yy from an array to a vector
vector<long double> YY;
YY.insert(YY.begin(), begin(yy), end(yy));
for(int i = 0; i<=nPoints -1; i++){
cout<<YY[i]<<endl;
}
return 0;
}
和工作代码
// Working Code: simply changed long double yy[nPoints] to long double yy[5]
#include <vector>
using namespace std;
int main(){
int nPoints = 5;
// initialize an input vector
vector<long double> xx = {1, 2, 3, 4, 5};
// compute some function of xx in a loop
long double yy[5];
for(int i = 0; i<=nPoints - 1; i++){
yy[i] = 2*xx[i];
}
// convert yy from an array to a vector
vector<long double> YY;
YY.insert(YY.begin(), begin(yy), end(yy));
for(int i = 0; i<=nPoints -1; i++){
cout<<YY[i]<<endl;
}
return 0;
}
第一个返回以下错误消息：
g++ -Wall testMain.cpp
testMain.cpp: In function 'int main()':
testMain.cpp:20:32: error: no matching function for call to 'begin(long double [nPoints])'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0bitsrange_access.h:36,
from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0initializer_list:89:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::begin(std::initializer_list<_Tp>)'
89 | begin(initializer_list<_Tp> __ils) noexcept
| ^~~~~
c:mingwincludec++9.1.0initializer_list:89:5: note: template argument deduction/substitution failed:
testMain.cpp:20:32: note: mismatched types 'std::initializer_list<_Tp>' and 'long double*'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:48:5: note: candidate: 'template<class _Container> decltype (__cont.begin()) std::begin(_Container&)'
48 | begin(_Container& __cont) -> decltype(__cont.begin())
| ^~~~~
c:mingwincludec++9.1.0bitsrange_access.h:48:5: note: template argument deduction/substitution failed:
testMain.cpp:20:32: note: variable-sized array type 'long double [nPoints]' is not a valid template argument
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:58:5: note: candidate: 'template<class _Container> decltype (__cont.begin()) std::begin(const _Container&)'
58 | begin(const _Container& __cont) -> decltype(__cont.begin())
| ^~~~~
c:mingwincludec++9.1.0bitsrange_access.h:58:5: note: template argument deduction/substitution failed:
testMain.cpp:20:32: note: variable-sized array type 'long double [nPoints]' is not a valid template argument
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:87:5: note: candidate: 'template<class _Tp, long long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
87 | begin(_Tp (&__arr)[_Nm])
| ^~~~~
c:mingwincludec++9.1.0bitsrange_access.h:87:5: note: template argument deduction/substitution failed:
testMain.cpp:20:32: note: variable-sized array type 'long long int' is not a valid template argument
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:104:31: note: candidate: 'template<class _Tp> _Tp* std::begin(std::valarray<_Tp>&)'
104 | template<typename _Tp> _Tp* begin(valarray<_Tp>&);
| ^~~~~
c:mingwincludec++9.1.0bitsrange_access.h:104:31: note: template argument deduction/substitution failed:
testMain.cpp:20:32: note: mismatched types 'std::valarray<_Tp>' and 'long double [nPoints]'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:105:37: note: candidate: 'template<class _Tp> const _Tp* std::begin(const std::valarray<_Tp>&)'
105 | template<typename _Tp> const _Tp* begin(const valarray<_Tp>&);
| ^~~~~
c:mingwincludec++9.1.0bitsrange_access.h:105:37: note: template argument deduction/substitution failed:
testMain.cpp:20:32: note: mismatched types 'const std::valarray<_Tp>' and 'long double [nPoints]'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
testMain.cpp:20:41: error: no matching function for call to 'end(long double [nPoints])'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0bitsrange_access.h:36,
from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0initializer_list:99:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)'
99 | end(initializer_list<_Tp> __ils) noexcept
| ^~~
c:mingwincludec++9.1.0initializer_list:99:5: note: template argument deduction/substitution failed:
testMain.cpp:20:41: note: mismatched types 'std::initializer_list<_Tp>' and 'long double*'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:68:5: note: candidate: 'template<class _Container> decltype (__cont.end()) std::end(_Container&)'
68 | end(_Container& __cont) -> decltype(__cont.end())
| ^~~
c:mingwincludec++9.1.0bitsrange_access.h:68:5: note: template argument deduction/substitution failed:
testMain.cpp:20:41: note: variable-sized array type 'long double [nPoints]' is not a valid template argument
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:78:5: note: candidate: 'template<class _Container> decltype (__cont.end()) std::end(const _Container&)'
78 | end(const _Container& __cont) -> decltype(__cont.end())
| ^~~
c:mingwincludec++9.1.0bitsrange_access.h:78:5: note: template argument deduction/substitution failed:
testMain.cpp:20:41: note: variable-sized array type 'long double [nPoints]' is not a valid template argument
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:97:5: note: candidate: 'template<class _Tp, long long unsigned int _Nm> constexpr _Tp* std::end(_Tp (&)[_Nm])'
97 | end(_Tp (&__arr)[_Nm])
| ^~~
c:mingwincludec++9.1.0bitsrange_access.h:97:5: note: template argument deduction/substitution failed:
testMain.cpp:20:41: note: variable-sized array type 'long long int' is not a valid template argument
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:106:31: note: candidate: 'template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)'
106 | template<typename _Tp> _Tp* end(valarray<_Tp>&);
| ^~~
c:mingwincludec++9.1.0bitsrange_access.h:106:31: note: template argument deduction/substitution failed:
testMain.cpp:20:41: note: mismatched types 'std::valarray<_Tp>' and 'long double [nPoints]'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
| ^
In file included from c:mingwincludec++9.1.0string:54,
from c:mingwincludec++9.1.0bitslocale_classes.h:40,
from c:mingwincludec++9.1.0bitsios_base.h:41,
from c:mingwincludec++9.1.0ios:42,
from c:mingwincludec++9.1.0ostream:38,
from c:mingwincludec++9.1.0iostream:39,
from testMain.cpp:1:
c:mingwincludec++9.1.0bitsrange_access.h:107:37: note: candidate: 'template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)'
107 | template<typename _Tp> const _Tp* end(const valarray<_Tp>&);
| ^~~
c:mingwincludec++9.1.0bitsrange_access.h:107:37: note: template argument deduction/substitution failed:
testMain.cpp:20:41: note: mismatched types 'const std::valarray<_Tp>' and 'long double [nPoints]'
20 | YY.insert(YY.begin(), begin(yy), end(yy));
问题 1
您缺少声明 std::begin 的头文件。
加
#include <iterator>
到您的文件。
问题2
long double yy[nPoints];
不是标准C++。一些编译器支持它作为扩展。
std::begin不适用于 VLA。它仅适用于标准数组 - 其大小在编译时已知的数组。
鉴于您可以将std::vector用于运行时已知大小的数组，因此无需使用 VLA。
而不是
long double yy[nPoints];
用
std::vector<long double> yy(nPoints);
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