我知道如何在其他语言中做到这一点,但在 C++ 中却不知道,我不得不在这里使用它。
我有一组字符串(keywords
)作为列表打印到 out
,字符串之间需要逗号,而不是尾随逗号。例如,在 Java 中,我会使用 StringBuilder
并在构建字符串后删除末尾的逗号。如何在 C++ 中做到这一点?
auto iter = keywords.begin();
for (iter; iter != keywords.end( ); iter++ )
{
out << *iter << ", ";
}
out << endl;
我最初尝试插入以下 block 来执行此操作(将逗号打印移至此处):
if (iter++ != keywords.end())
out << ", ";
iter--;
最佳答案
使用中缀迭代器:
// infix_iterator.h
//
// Lifted from Jerry Coffin's 's prefix_ostream_iterator
#if !defined(INFIX_ITERATOR_H_)
#define INFIX_ITERATOR_H_
#include <ostream>
#include <iterator>
template <class T,
class charT=char,
class traits=std::char_traits<charT> >
class infix_ostream_iterator :
public std::iterator<std::output_iterator_tag,void,void,void,void>
{
std::basic_ostream<charT,traits> *os;
charT const* delimiter;
bool first_elem;
public:
typedef charT char_type;
typedef traits traits_type;
typedef std::basic_ostream<charT,traits> ostream_type;
infix_ostream_iterator(ostream_type& s)
: os(&s),delimiter(0), first_elem(true)
{}
infix_ostream_iterator(ostream_type& s, charT const *d)
: os(&s),delimiter(d), first_elem(true)
{}
infix_ostream_iterator<T,charT,traits>& operator=(T const &item)
{
// Here's the only real change from ostream_iterator:
// Normally, the '*os << item;' would come before the 'if'.
if (!first_elem && delimiter != 0)
*os << delimiter;
*os << item;
first_elem = false;
return *this;
}
infix_ostream_iterator<T,charT,traits> &operator*() {
return *this;
}
infix_ostream_iterator<T,charT,traits> &operator++() {
return *this;
}
infix_ostream_iterator<T,charT,traits> &operator++(int) {
return *this;
}
};
#endif
用法类似于:
#include "infix_iterator.h"
// ...
std::copy(keywords.begin(), keywords.end(), infix_iterator(out, ","));
关于c++ - 如何打印以逗号分隔的元素列表?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3496982/