設計&程式

Because the loop only runs until no more space is found.
to output last:


Code:

string str = "1.roger 2.chunag 3.abc 4.ccc";
size_t pos = str.find(" "); // indexof of _first_ space
size_t oldPos = 0;
while (pos != string::npos)
{
string piece = str.substr(oldPos, pos - oldPos);
cout << piece << endl;
oldPos = pos + 1;
pos = str.find(" ", oldPos);
}
cout << str.substr(oldPos) << endl;


It can't be that hard for yourself to read about the string class.

Because at the point when you have processed the "3.abc" segment, you store oldPos = pos + 1.

Then:


Code:
pos = str.find(" ", oldPos)



is searching only on the part of the string: "4.ccc".

There are no spaces in that string, so find() will return string::npos, your loop exits and the program eventually exits.

If you add the following immediately after the closing brace of the while() loop:


Code:
if (pos == string::npos && oldPos != 0) cout << str.substr(oldPos) << endl;

Use replace this method

string str1 = "1.roger 2.chunag 3.abc 4.ccc";
replace(str1.begin(), str1.end(), ' ', '\n');
cout << str1 << endl;

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