nonprint character

[Vegertar]

//发现无法彻底删除连续出现且相等的非打印字符, 更疑惑的是居然连计数器都发生了变化.
//下面是代码 :
#include <iostream>
#include <cctype>

using namespace std;

int main()
{
    string expression("a\t\tb\n\nc");
    cout << expression << endl;

    int count = 0;
    for (std::string::iterator i = expression.begin(); i != expression.end(); ++i)
        if (!isprint(*i)) {
            ++count;
            //expression.erase(i);
        }

    cout << "nonprint character counting : " << count << endl;
    cout << expression << endl;
}

再看看运行结果:

去除注释前

a		b

c
nonprint character counting : 4
a		b

c

去除注释后

a		b

c
nonprint character counting : 2
a	b
c

何解?

[Longinc]

执行expression.erase(i)后expression的长度发生变化（-1），而i值没有变导致删除提一个\t后紧跟他后面的\t向前进一位没有做处理

[Fighting Horse]

	for (std::string::iterator i = expression.begin(); i != expression.end(); ) {
		if (!isprint(*i)) {
			++count;
			i = expression.erase(i);
		} else
			i++;
	}

因为string是数组，erase(i)后，后面的元素向前移动，i实际上已经指向下一个了，这一点和链表不一样，为了统一，stl用erase的返回值来表示下一个元素

[太乙]

//发现无法彻底删除连续出现且相等的非打印字符, 更疑惑的是居然连计数器都发生了变化.
//下面是代码 :
#include <iostream>
#include <string>
#include <cctype>

using namespace std;

int main()
{
    string expression("a\t\tb\n\nc");
    cout << expression << endl;

    int count = 0;
    for (std::string::iterator i = expression.begin(); i != expression.end();)
        if (!isprint(*i)) {
            ++count;
            i  = expression.erase(i);//erase导致迭代器失效
        }
		else
			 ++i;

    cout << "nonprint character counting : " << count << endl;
    cout << expression << endl;
}

[simonyuan]

1楼是正解

[Vegertar]

晕死, 当前迭代器已经失效!多谢!