4
我試圖編寫一個代碼來從名爲「test.txt」的文件中讀取字符串並將字符串寫入標準輸出。下面的代碼工作得很好:爲什麼istream_iterator <string>(ifstream(「test.txt」))會導致錯誤?
int main()
{
using namespace std;
ifstream file("test.txt");
copy(istream_iterator<string>(file),
istream_iterator<string>(),
ostream_iterator<string>(cout, " "));
}
然而,這種修改,代碼不再編譯:
int main()
{
using namespace std;
copy(istream_iterator<string>(ifstream("test.txt")), // <-- Error here
istream_iterator<string>(),
ostream_iterator<string>(cout, " "));
}
爲什麼沒有這個版本的編譯?
我使用的編譯器是G ++ 4.6.2,錯誤如下:
ex11-16.cpp:16:65: error: no matching function for call to 'std::istream_iterator<std::basic_string<char> >::istream_iterator(std::ifstream)'
ex11-16.cpp:16:65: note: candidates are:
.../bits/stream_iterator.h:72:7: note: std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_iterator(const std::istream_iterator<_Tp, _CharT, _Traits, _Dist>&) [with _Tp = std::basic_string<char>, _CharT = char, _Traits = std::char_traits<char>, _Dist = int, std::istream_iterator<_Tp, _CharT, _Traits, _Dist> = std::istream_iterator<std::basic_string<char> >]
.../bits/stream_iterator.h:72:7: note: no known conversion for argument 1 from 'std::ifstream {aka std::basic_ifstream<char>}' to 'const std::istream_iterator<std::basic_string<char> >&'
.../bits/stream_iterator.h:68:7: note: std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_iterator(std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_type&) [with _Tp = std::basic_string<char>, _CharT = char, _Traits = std::char_traits<char>, _Dist = int, std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_type = std::basic_istream<char>]
.../bits/stream_iterator.h:68:7: note: no known conversion for argument 1 from 'std::ifstream {aka std::basic_ifstream<char>}' to 'std::istream_iterator<std::basic_string<char> >::istream_type& {aka std::basic_istream<char>&}'
.../bits/stream_iterator.h:64:26: note: std::istream_iterator<_Tp, _CharT, _Traits, _Dist>::istream_iterator() [with _Tp = std::basic_string<char>, _CharT = char, _Traits = std::char_traits<char>, _Dist = int]
.../bits/stream_iterator.h:64:26: note: candidate expects 0 arguments, 1 provided
*甚至不能編譯* - 至少應該給我們提供錯誤。 – chris
在第二個例子中'ifstream(test.txt)'應該是'ifstream(「test.txt)''或者你應該編輯你的問題以包含正確的代碼。 –