C++语法基础--泛型算法（generic algorithm)--写入容器元素的算法fill(),fill_n,replace()
2013-07-12 04:33
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*fill
Assigns val to all the elements in the range [first,last)
原型：
template <class ForwardIterator, class T>
void fill (ForwardIterator first, ForwardIterator last, const T& val);
该算法等效于：
template <class ForwardIterator, class T>
void fill (ForwardIterator first, ForwardIterator last, const T& val)
{
while (first != last) {
*first = val;
++first;
}
}
Example:
int main ()
{
vector<int> myvector (8); // myvector: 0 0 0 0 0 0 0 0
fill (myvector.begin(),myvector.begin()+4,1);
// myvector: 1 1 1 1 0 0 0 0
fill (myvector.begin()+3,myvector.end()-2,2); // myvector: 1 1 1 2 2 2 0 0
//myvector contains:
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it;// 1 1 1 2 2 2 0 0
}
return 0;
}
*fill_n
Assigns val to the first n elements of the sequence pointed by first.
原型：
template <class OutputIterator, class Size, class T>
void fill_n (OutputIterator first, Size n, const T& val);
该算法等效于：
template <class OutputIterator, class Size, class T>
OutputIterator fill_n (OutputIterator first, Size n, const T& val)
{
while (n>0) {
*first = val;
++first; --n;
}
return first; // since C++11
}
Example:
int main ()
{
vector<int> myvector (8,1); // myvector: 1 1 1 1 1 1 1 1
std::fill_n (myvector.begin(),4,2); // myvector: 2 2 2 2 1 1 1 1
//myvector contains:
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it;//2 2 2 2 1 1 1 1
}
return 0;
}
Tips:
fill_n假定对指定数量的元素做写操作时是安全的，所以要确保容器有足够的空间。
*replace
Assigns new_value to all the elements in the range [first,last) that compare equal to old_value.
原型：
template <class ForwardIterator, class T>
void replace (ForwardIterator first, ForwardIterator last,
const T& old_value, const T& new_value);
该算法等效于：
template <class ForwardIterator, class T>
void replace (ForwardIterator first, ForwardIterator last,
const T& old_value, const T& new_value)
{
while (first!=last) {
if (*first == old_value) *first=new_value;
++first;
}
}
Example:
int main ()
{
int myints[] = { 1,1,1,3,2,2,1,3 };
vector<int> myvector (myints, myints+8); // 1,1,1,3,2,2,1,3
replace (myvector.begin(), myvector.end(), 3, 2);// 1,1,1,2,2,2,1,2
//myvector contains:
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it;// 1,1,1,2,2,2,1,2
}
return 0;
}
Assigns val to all the elements in the range [first,last)
原型：
template <class ForwardIterator, class T>
void fill (ForwardIterator first, ForwardIterator last, const T& val);
该算法等效于：
template <class ForwardIterator, class T>
void fill (ForwardIterator first, ForwardIterator last, const T& val)
{
while (first != last) {
*first = val;
++first;
}
}
Example:
int main ()
{
vector<int> myvector (8); // myvector: 0 0 0 0 0 0 0 0
fill (myvector.begin(),myvector.begin()+4,1);
// myvector: 1 1 1 1 0 0 0 0
fill (myvector.begin()+3,myvector.end()-2,2); // myvector: 1 1 1 2 2 2 0 0
//myvector contains:
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it;// 1 1 1 2 2 2 0 0
}
return 0;
}
*fill_n
Assigns val to the first n elements of the sequence pointed by first.
原型：
template <class OutputIterator, class Size, class T>
void fill_n (OutputIterator first, Size n, const T& val);
该算法等效于：
template <class OutputIterator, class Size, class T>
OutputIterator fill_n (OutputIterator first, Size n, const T& val)
{
while (n>0) {
*first = val;
++first; --n;
}
return first; // since C++11
}
Example:
int main ()
{
vector<int> myvector (8,1); // myvector: 1 1 1 1 1 1 1 1
std::fill_n (myvector.begin(),4,2); // myvector: 2 2 2 2 1 1 1 1
//myvector contains:
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it;//2 2 2 2 1 1 1 1
}
return 0;
}
Tips:
fill_n假定对指定数量的元素做写操作时是安全的，所以要确保容器有足够的空间。
*replace
Assigns new_value to all the elements in the range [first,last) that compare equal to old_value.
原型：
template <class ForwardIterator, class T>
void replace (ForwardIterator first, ForwardIterator last,
const T& old_value, const T& new_value);
该算法等效于：
template <class ForwardIterator, class T>
void replace (ForwardIterator first, ForwardIterator last,
const T& old_value, const T& new_value)
{
while (first!=last) {
if (*first == old_value) *first=new_value;
++first;
}
}
Example:
int main ()
{
int myints[] = { 1,1,1,3,2,2,1,3 };
vector<int> myvector (myints, myints+8); // 1,1,1,3,2,2,1,3
replace (myvector.begin(), myvector.end(), 3, 2);// 1,1,1,2,2,2,1,2
//myvector contains:
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
{
cout << ' ' << *it;// 1,1,1,2,2,2,1,2
}
return 0;
}
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