Quá tải >> ifstream_iterator cho các cặp

Question

Tôi đang cố gắng tạo ifstream_iterator trên cặp. Mã của tôi là như sau:

typedef pair<float, int> T; 

istream& operator>>(istream& stream, T& in) { 
    stream >> in.first >> in.second; 
    return stream; 
} 


int main(int argc, char **argv) { 
    ifstream infile("dummy2"); 
    istream_iterator<T> iit(infile); 
    istream_iterator<T> eos; 
    while (iit != eos) { 
     cout << (*iit).first << endl; 
     ++iit; 
    } 
    return 0; 
} 

Tôi có một tập tin dummy "dummy2" như sau:

"a" 4 "b" 5 

Tôi muốn đầu ra cặp { "a", 4} và { "b", 5}.

Tuy nhiên, tôi nhận được lỗi biên soạn khó chịu

In file included from /usr/include/c++/4.6/iterator:66:0, 
       from filestream.cpp:9: 
/usr/include/c++/4.6/bits/stream_iterator.h: In member function ‘void std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::_M_read() [with _Tp = std::pair<float, int>, _CharT = char, _Traits = std::char_traits<char>, _Dist = long int]’: 
/usr/include/c++/4.6/bits/stream_iterator.h:70:9: instantiated from ‘std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_iterator(std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_type&) [with _Tp = std::pair<float, int>, _CharT = char, _Traits = std::char_traits<char>, _Dist = long int, std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_type = std::basic_istream<char>]’ 
filestream.cpp:32:33: instantiated from here 
/usr/include/c++/4.6/bits/stream_iterator.h:121:6: error: no match for ‘operator>>’ in ‘*((std::istream_iterator<std::pair<float, int> >*)this)->std::istream_iterator<std::pair<float, int> >::_M_stream >> ((std::istream_iterator<std::pair<float, int> >*)this)->std::istream_iterator<std::pair<float, int> >::_M_value’ 
/usr/include/c++/4.6/bits/stream_iterator.h:121:6: note: candidates are: 
/usr/include/c++/4.6/istream:122:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:122:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}’ 
/usr/include/c++/4.6/istream:126:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>, std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>] 
/usr/include/c++/4.6/istream:126:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}’ 
/usr/include/c++/4.6/istream:133:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:133:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘std::ios_base& (*)(std::ios_base&)’ 
/usr/include/c++/4.6/istream:169:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:169:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘bool&’ 
/usr/include/c++/4.6/istream:173:7: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char, _Traits = std::char_traits<char>] 
/usr/include/c++/4.6/istream:173:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘short int&’ 
/usr/include/c++/4.6/istream:176:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:176:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘short unsigned int&’ 
/usr/include/c++/4.6/istream:180:7: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char, _Traits = std::char_traits<char>] 
/usr/include/c++/4.6/istream:180:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘int&’ 
/usr/include/c++/4.6/istream:183:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:183:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘unsigned int&’ 
/usr/include/c++/4.6/istream:187:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:187:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘long int&’ 
/usr/include/c++/4.6/istream:191:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:191:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘long unsigned int&’ 
/usr/include/c++/4.6/istream:196:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:196:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘long long int&’ 
/usr/include/c++/4.6/istream:200:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:200:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘long long unsigned int&’ 
/usr/include/c++/4.6/istream:205:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:205:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘float&’ 
/usr/include/c++/4.6/istream:209:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:209:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘double&’ 
/usr/include/c++/4.6/istream:213:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:213:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘long double&’ 
/usr/include/c++/4.6/istream:217:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] 
/usr/include/c++/4.6/istream:217:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘void*&’ 
/usr/include/c++/4.6/istream:241:7: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>] 
/usr/include/c++/4.6/istream:241:7: note: no known conversion for argument 1 from ‘std::pair<float, int>’ to ‘std::basic_istream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}’ 
/usr/include/c++/4.6/bits/basic_string.tcc:998:5: note: template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::basic_string<_CharT, _Traits, _Alloc>&) 
/usr/include/c++/4.6/bits/random.tcc:923:5: note: template<class _IntType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::uniform_int_distribution<_IntType>&) 
/usr/include/c++/4.6/bits/random.tcc:968:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::uniform_real_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:1890:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::cauchy_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.h:3381:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::bernoulli_distribution&) 
/usr/include/c++/4.6/bits/random.tcc:1733:5: note: template<class _RealType1, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::normal_distribution<_RealType1>&) 
/usr/include/c++/4.6/bits/random.tcc:1063:5: note: template<class _IntType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::geometric_distribution<_IntType>&) 
/usr/include/c++/4.6/bits/random.tcc:2085:5: note: template<class _RealType1, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::gamma_distribution<_RealType1>&) 
/usr/include/c++/4.6/bits/random.tcc:1622:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::exponential_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:2143:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::weibull_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:2200:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::extreme_value_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:194:5: note: template<class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::linear_congruential_engine<_UIntType, __a, __c, __m>&) 
/usr/include/c++/4.6/bits/random.tcc:491:5: note: template<class _UIntType, long unsigned int __w, long unsigned int __n, long unsigned int __m, long unsigned int __r, _UIntType __a, long unsigned int __u, _UIntType __d, long unsigned int __s, _UIntType __b, long unsigned int __t, _UIntType __c, long unsigned int __l, _UIntType __f, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>&) 
/usr/include/c++/4.6/bits/random.tcc:642:5: note: template<class _UIntType, long unsigned int __w, long unsigned int __s, long unsigned int __r, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::subtract_with_carry_engine<_UIntType, __w, __s, __r>&) 
/usr/include/c++/4.6/bits/random.tcc:709:5: note: template<class _RandomNumberEngine, long unsigned int __p, long unsigned int __r, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::discard_block_engine<_RandomNumberEngine, __p, __r>&) 
/usr/include/c++/4.6/bits/random.tcc:815:5: note: template<class _RandomNumberEngine, long unsigned int __k, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::shuffle_order_engine<_RandomNumberEngine, __k>&) 
/usr/include/c++/4.6/bits/random.tcc:1138:5: note: template<class _IntType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::negative_binomial_distribution<_IntType>&) 
/usr/include/c++/4.6/bits/random.tcc:1328:5: note: template<class _IntType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::poisson_distribution<_IntType>&) 
/usr/include/c++/4.6/bits/random.tcc:1577:5: note: template<class _IntType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::binomial_distribution<_IntType>&) 
/usr/include/c++/4.6/bits/random.tcc:1782:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::lognormal_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:1827:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::chi_squared_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:1936:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::fisher_f_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:1981:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::student_t_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:2308:5: note: template<class _IntType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::discrete_distribution<_IntType>&) 
/usr/include/c++/4.6/bits/random.tcc:2488:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::piecewise_constant_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/random.tcc:2690:5: note: template<class _RealType, class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::piecewise_linear_distribution<_RealType>&) 
/usr/include/c++/4.6/bits/istream.tcc:957:5: note: template<class _CharT2, class _Traits2> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT2*) 
/usr/include/c++/4.6/bits/istream.tcc:925:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT&) 
/usr/include/c++/4.6/istream:709:5: note: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char&) 
/usr/include/c++/4.6/istream:714:5: note: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char&) 
/usr/include/c++/4.6/istream:756:5: note: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*) 
/usr/include/c++/4.6/istream:761:5: note: template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*) 
/usr/include/c++/4.6/istream:852:5: note: std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&&, _Tp&) [with _CharT = char, _Traits = std::char_traits<char>, _Tp = std::pair<float, int>] <near match> 
/usr/include/c++/4.6/istream:852:5: note: no known conversion for argument 1 from ‘std::istream_iterator<std::pair<float, int> >::istream_type {aka std::basic_istream<char>}’ to ‘std::basic_istream<char>&&’ 
/usr/include/c++/4.6/iomanip:70:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Resetiosflags) 
/usr/include/c++/4.6/iomanip:100:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Setiosflags) 
/usr/include/c++/4.6/iomanip:131:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Setbase) 
/usr/include/c++/4.6/iomanip:169:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Setfill<_CharT>) 
/usr/include/c++/4.6/iomanip:199:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Setprecision) 
/usr/include/c++/4.6/iomanip:229:5: note: template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Setw) 
/usr/include/c++/4.6/iomanip:263:5: note: template<class _CharT, class _Traits, class _MoneyT> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::_Get_money<_MoneyT>) 
make: *** [filestream] Error 1 

tôi không thể khá có ý nghĩa về những gì đang xảy ra ở đây. Bất kỳ trợ giúp được đánh giá cao. Cảm ơn rất nhiều!

Answer 1

Bạn sẽ lưu ý rằng chỉ cần làm điều này:

T t; 
infile >> t; 

trình như một say mê! Chuyện gì vậy?

std::pair được khai báo trong không gian tên std.

istream_iterator<> sử dụng operator>> thực sự, và nó nên sử dụng ADL lúc instantiation (điều này được gọi là hai pha-lookup).

Tuy nhiên, vào thời điểm instantiation, nó sẽ không xem xét operator>> của bạn vì nó không tồn tại trong không gian tên mà thực hiện istream_iterator và không phải là nó tuyên bố trong bất kỳ namespaces liên ngụ ý của các đối số (đây là ADL bậc thang).

Bạn có thể bị cám dỗ "sửa chữa" nó bằng cách định nghĩa tình trạng quá tải của bạn trong không gian tên std (và nó hoạt động) nhưng điều đó không được phép theo tiêu chuẩn và kỹ thuật dẫn đến Undefined Behaviour.

Vì vậy, bạn muốn làm tốt hơn để giới thiệu một loại cho phép ADL đá trong:

struct T : public std::pair<int,float> {}; 

Live On Coliru

#include <utility> 
#include <iostream> 
#include <iterator> 

struct T : std::pair<float, int> { 
    using std::pair<float, int>::pair; 
}; 

std::istream& operator>>(std::istream& stream, T& in) { 
    return stream >> in.first >> in.second; 
} 

int main() { 
    std::istream_iterator<T> iit(std::cin); 
    std::istream_iterator<T> eos; 
    while (iit != eos) { 
     std::cout << (*iit).first << std::endl; 
     ++iit; 
    } 
} 

---

Tôi nghi ngờ rằng về mặt lý thuyết bạn nên có có thể lừa điều bằng cách sắp xếp lại bao gồm và tiêm quá tải sớm đủ để nó là "vi sible "trong giai đoạn đầu của tra cứu tên. Tuy nhiên, cho dù tùy chọn này có sẵn hay không tùy thuộc vào việc triển khai và nếu bạn không may mắn, bạn vẫn không thể đạt được mà không thay đổi tiêu đề thư viện chuẩn (không làm điều đó).

Answer 2

Đây là một vấn đề khá phổ biến, mà không có giải pháp thực sự rõ ràng.Một thường làm là đặt nhà điều hành của bạn vào namespace std:

typedef pair<float, int> T; 

namespace std { 
    istream& operator>>(istream& stream, T& in) { 
     stream >> in.first >> in.second; 
     return stream; 
    } 
} 

int main(int argc, char **argv) { 
    ifstream infile("dummy2"); 
    istream_iterator<T> iit(infile); 
    istream_iterator<T> eos; 
    while (iit != eos) { 
     cout << (*iit).first << endl; 
     ++iit; 
    } 
    return 0; 
} 

chính thức, điều này mang đến cho hành vi undefined - bạn có thể thêm một số chuyên ngành để namespace std, nhưng bạn không thể thêm quá tải ở đó. Không chính thức, tôi chưa thấy một trình biên dịch/thư viện nơi nó gây ra một vấn đề.