Sorting array of strings causes seg fault - c++

Question

I'm trying to write a sort to sort an array of strings in ascending order I have the function as:
void mySort(string list[], int size) {
for (int i=0; i<size; i++){
for (int j=0; j < size-i; j++){
if (strcmp(list[j].c_str(),list[j+1].c_str())< 0);{
std::swap(list[j], list[j + 1]);
}
}
}
}
and then the function that uses the sort:
void q0run(question q){
std::string input = q.programInput; //Place the data file in a variable
//cout << input << endl; //Test to make sure data file stored correctly - works
std::ifstream inputFile (input.c_str()); //Open File
if(inputFile.good()){ //Make sure file is open before trying to work with it
//Begin Working with information
cout << "In File: \t" << input << endl;
int number_of_lines = 0;
std::string line;
while (std::getline(inputFile, line)){
++number_of_lines;
}
std::cout << "Number of lines in text file: " << number_of_lines << endl;
std::string dataStorage[number_of_lines];
inputFile.clear();
inputFile.seekg(0);
for(int loop=0;loop<number_of_lines;loop++){
getline(inputFile,dataStorage[loop]);
}
mySort(dataStorage,number_of_lines);
for(int loop=0;loop<number_of_lines;loop++){
cout << dataStorage[loop] << endl;
}
inputFile.close();
}else{
cout << "Could not open file!!!" << endl;
}
}
When I run the program though it segfaults at the sort. Not sure what I'm doing wrong:
In File: data01a.txt
Number of lines in text file: 253
Segmentation fault (core dumped)
The array to be sorted is being populated, I can run a loop on it and print it all out unsorted, any ideas? An easier sorting method will be fine too! Thanks!

Answer 1

if (strcmp(list[j].c_str(),list[j+1].c_str())< 0);{
Oops!
There's an extra ; so the swap will always occur;
Your inner loop needs one fewer iterations, otherwise j+1 jumps off the end;
And are all those C-string conversions really necessary?
std::string::compare would do the job...

Answer 2

The actual bug in your code was answered in a comment.
Your "j+1" index can be out of bounds and in the first iteration it is. You therefore need to loop j up to size-i-1 or iterate i from 1 onward, thus..
for (int i=1; i<size; i++)
I assume this is some kind of exercise as the correct way to sort is simply to use std::sort.
You have also been offered alternative ways to compare two strings, the simplest of which is just its overloaded operator<, thus
if( list[j] < list[j+1] )

Answer 3

You have an out of bounds access which may be the cause
for (int i=0; i<size; i++){
for (int j=0; j < size-i; j++){
if (strcmp(list[j].c_str(),list[j+1].c_str())< 0){
std::swap(list[j], list[j + 1]);
}
On the first iteration you have
i=0; j=size-1 =>strcmp(list[size-1].c_str(),list[size])
change the stop condition in the first loop:
for (int i=0; i<size-1; i++){
for (int j=0; j < size-i; j++){
if (strcmp(list[j].c_str(),list[j+1].c_str())< 0){
std::swap(list[j], list[j + 1]);
}
hope this helps.

Answer 4

This code does what you want in C++11:
#include <algorithm>
#include <iostream>
#include <array>
#include <string>
using namespace std;
int main()
{
string s1 = "hello";
string s2 = "world!";
string s3 = "peanut";
string s4 = "butter";
array<string,4> ar = {s1,s2,s3,s4};
sort(ar.begin(),ar.end());
for(auto elem : ar)
cout << elem << endl;
return 0;
}