How to iterate through a List function? - c++

Question

I'm running a test program where I make a list of strings and try to find which strings have a certain suffix or prefix.
#include <iostream>
#include <list>
#include <string>
using namespace std;
list<string> beginWith(const string& pre, list <string> test);
list<string> endWith(const string& suf,list <string> test);
int main(){
list <string> testList(5);
string suffix = "able";
string prefix = "M";
testList.push_back("Agreeable");
testList.push_back("Doable");
testList.push_back("Machine");
testList.push_back("Makeable");
testList.push_back("Available");
for(list <string>::const_iterator it = testList.begin(); it != testList.end(); it++){
cout << *it << endl;
}
for(list <string>::const_iterator it = beginWith(prefix, testList).begin(); it != beginWith(prefix, testList).end(); it++){
cout << *it << endl;
}
for(list <string>::const_iterator it = endWith(suffix, testList).begin(); it != endWith(suffix, testList).end(); it++){
cout << *it << endl;
}
return 0;
}
list<string> beginWith(const string& pre, list<string> test){
list <string> answer;
for(list <string>::const_iterator it = test.begin(); it != test.end(); it++){
if(pre == it->substr(0, pre.length())){
answer.push_back(*it);
}
}
return answer;
}
list<string> endWith(const string& suf, list <string> test){
list <string> answer;
for(list <string>::const_iterator it = test.begin(); it != test.end(); it++){
if(suf == it->substr(it->length() - suf.length() , it->back())){
answer.push_back(*it);
}
}
return answer;
}
I declared a list of strings printed them out with the first for-loop. I also have 2 functions which will iterate through that list and then return a list of strings that have a certain prefix or suffix. I'll print those out with the 2nd and 3rd for-loop. The 1st for-loop prints out correctly however, I get a segmentation fault: 11 when I print out the 2nd and 3rd for loops. I'm confused as to how I would get those for-loops to iterate through the list functions and print out the contents.

Answer 1

beginWith and endWith return a list by value. This makes the for-loops call begin() and end() on different copies of the list.

Answer 2

list<string> beginWith(const string& pre, list<string> test) {
list <string> answer;
for (auto word : test) // Use C++ auto to iterate collection
{
cout << "Testing " << word << " against " << pre << " ... ";
if (word.find(pre) == 0) // From http://thispointer.com/c-check-if-a-string-starts-with-an-another-given-string/
{
cout << "match!";
answer.push_back(word);
}
cout << '\n';
}
return answer;
}
list<string> endWith(const string& suf, list <string> test) {
list <string> answer;
for (auto word : test)
{
cout << "Testing " << word << " against " << suf << " ... ";
if (word.size() >= suf.size() &&
word.compare(word.size() - suf.size(), suf.size(), suf) == 0) // From http://thispointer.com/c-how-to-check-if-a-string-ends-with-an-another-given-string/
{
cout << "match!";
answer.push_back(word);
}
cout << '\n';
}
return answer;
}
int main(int argc, wchar_t *argv[])
{
list <string> testList {}; // Create empty list, not list with five elements
string suffix = "able";
string prefix = "M";
testList.push_back("Agreeable");
testList.push_back("Doable");
testList.push_back("Machine");
testList.push_back("Makeable");
testList.push_back("Available");
for (auto word : testList) {
cout << word << '\n';
}
auto prefixedWords = beginWith(prefix, testList);
cout << "Prefixed words: \n";
for (auto prefixed : prefixedWords) {
cout << " " << prefixed << '\n';
}
auto suffixedWords = endWith(suffix, testList);
cout << "Suffixed words: \n";
for (auto suffixed : suffixedWords) {
cout << " " << suffixed << '\n';
}
return 0;
}
Program output:
Agreeable
Doable
Machine
Makeable
Available
Testing Agreeable against M ...
Testing Doable against M ...
Testing Machine against M ... match!
Testing Makeable against M ... match!
Testing Available against M ...
Prefixed words:
Machine
Makeable
Testing Agreeable against able ... match!
Testing Doable against able ... match!
Testing Machine against able ...
Testing Makeable against able ... match!
Testing Available against able ... match!
Suffixed words:
Agreeable
Doable
Makeable
Available