I've created a function to run through a vector of strings and remove any strings of length 3 or less. This is a lesson in using the STL Algorithm library.
I'm having trouble in that the functions work but not only does it delete strings of length 3 or less but it also appends the string "vector" to the end.
The output should be
This test vector
and instead it is
This test vector vector"
How can I fix it?
/*
* using remove_if and custom call back function, write RemoveShortWords
* that accepts a vector<string> and removes all strings of length 3 or
* less from it. *shoot for 2 lines of code in functions.
*/
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iterator>
using namespace std;
bool StringLengthTest(string test) //test condition for remove_if algo.
{
return test.length() <= 3;
}
void RemoveShortWords(vector<string> &myVector)
{
//erase anything in vector with length <= 3
myVector.erase(remove_if(myVector.begin(),
myVector.end(),
StringLengthTest));
}
int main ()
{
//add some strings to vector
vector<string> myVector;
myVector.push_back("This");
myVector.push_back("is");
myVector.push_back("a");
myVector.push_back("test");
myVector.push_back("vector");
//print out contents of myVector (debugging)
copy(myVector.begin(), myVector.end(), ostream_iterator<string>(cout," "));
cout << endl; //flush the stream
RemoveShortWords(myVector); //remove words with length <= 3
//print out myVector (debugging)
copy(myVector.begin(), myVector.end(), ostream_iterator<string>(cout," "));
cout << endl;
system("pause");
return 0;
}
It is easiest to understand this if you seperate the statements:
auto iter(remove_if(myVector.begin(), myVector.end(), StringLengthTest));
myVector.erase(iter);
These 2 lines do the same as your single line. And it should be clear now what the "bug" is. remove_if, works first. It iterates over the whole vector and moves all "selected" entries "to the end" (better said: it moves the non selected entries to the front). After it has run it returns an iterator to the "last" position of the left over entries, something like:
this
test
vector
test <- iterator points here
vector
Then you run erase with a single iterator. That means you erase a single element pointed at - so you erase the "test" element. - What is left over is what you are seeing.
To fix it simply erase from the vector returned by remove_if to the end().:
myVector.erase(remove_if(myVector.begin(), myVector.end(), StringLengthTest), myVector.end()); //erase anything in vector with length <= 3
You should be using the two parameter form of erase:
myVector.erase(remove_if(myVector.begin(), myVector.end(), StringLengthTest),
myVector.end());
来源:https://stackoverflow.com/questions/9053883/erase-after-performing-remove-if