Alternative to strcmp() to alphabetically sort strings - c++

Question

stuType Class:
#include<iostream>
#include<cstring>
using namespace std;
#ifndef STUTYPE
#define STUTYPE
class stuType {
private:
string fname;
string lname;
string social;
float gpa;
public:
stuType(void) {
fname = "no_fname";
lname = "no_lname";
social = "no_social";
gpa = 0.0;
}
stuType(string fname_in, string lname_in, string social_in, float gpa_in) {
fname = fname_in;
lname = lname_in;
social = social_in;
gpa = gpa_in;
}
~stuType() {
//Nothing needs to be added here.
}
void set_fname(string new_fname) {
fname = new_fname;
}
void set_lname(string new_lname) {
lname = new_lname;
}
void set_ssn(string new_ssn) {
social = new_ssn;
}
void set_gpa(float new_gpa) {
gpa = new_gpa;
}
string get_fname(void) {
return fname;
}
string get_lname(void) {
return lname;
}
string get_ssn(void) {
return social;
}
float get_gpa(void) {
return gpa;
}
friend istream & operator>>(istream &in, stuType &stu) {
in>>stu.fname;
in>>stu.lname;
in>>stu.social;
in>>stu.gpa;
return in;
}
};
#endif
Sort.cpp:
#include<iostream>
#include<fstream>
#include<cstdlib>
#include<cstring>
#include"stuType.h"
using namespace std;
/*Loads the elements of the object instance with data from the input file.*/
void load(istream &input, stuType Student[], int *size);
/*Used in combination with the shellSort method to exchange the values of two variables in the class object.*/
void exchange(stuType &a, stuType &b);
/*Sorts the objects in ascending order by comparing the values of the lname strings between object indices.*/
void shellSort(stuType Student[], int size);
int main() {
stuType Student[10];
int size;
char inputFile[200];
char outputFile[200];
ifstream input;
ofstream output;
cout<<"[INPUT_FILE]: ";
cin>>inputFile;
cout<<"[OUTPUT_FILE]: ";
cin>>outputFile;
input.open(inputFile);
output.open(outputFile);
if (input.fail()) {
cerr<<"\n[FILE] Error opening '"<<inputFile<<"'"<<endl;
exit(1);
}
if (output.fail()) {
cerr<<"\n[FILE] Error opening '"<<outputFile<<"'"<<endl;
exit(1);
}
load(input, Student, &size);
shellSort(Student, size);
return 0;
}
void load(istream &input, stuType Student[], int *size) {
int length = 0, i = 0;
float gpa;
string social;
string fname;
string lname;
while(input >> social >> fname >> lname >> gpa) {
cout<<"[Node::Load] Setting 'social' for index ["<<i<<"] to "<<social<<endl;
Student[i].set_ssn(social);
cout<<"[Node::Load] Setting 'fname' for index ["<<i<<"] to "<<fname<<endl;
Student[i].set_fname(fname);
cout<<"[Node::Load] Setting 'lname' for index ["<<i<<"] to "<<lname<<endl;
Student[i].set_lname(lname);
cout<<"[Node::Load] Setting 'gpa' for index ["<<i<<"] to "<<gpa<<endl;
Student[i].set_gpa(gpa);
cout<<"[Node::Load] Incrementing 'length'..."<<endl;
length++;
cout<<"[Node::Load] Incrementing 'i'..."<<endl;
i++;
}
cout<<"==================================="<<endl;
for (int i = 0; i<length; i++) {
cout<<"[ENTRY] Index: "<<i<<" | SSN: "<<Student[i].get_ssn()<<" | fname: "<<Student[i].get_fname()<<" | lname: "<<Student[i].get_lname()<<" | gpa: "<<Student[i].get_gpa()<<endl;
}
cout<<"==================================="<<endl;
*size = length;
}
void exchange(stuType &a, stuType &b) {
stuType *temp;
*temp = a;
a = b;
b = *temp;
delete temp;
}
void shellSort(stuType Student[], int size) {
int gap = size/2;
bool passOK;
while(gap>0) {
passOK = true;
for(int i = 0; i<size-gap; i++) {
if (strcmp(Student[i].get_lname(), Student[i+gap].get_lname)>0) {
cout<<"[Node::Sort] Exchanging Index ["<<i<<"] with Index ["<<i+gap<<"]..."<<endl;
exchange(Student[i], Student[i+gap]);
passOK = false;
} else if (strcmp(Student[i].get_lname(), Student[i+gap].get_lname())==0) {
if (strcmp(Student[i].get_fname(), Student[i+gap].get_fname())>0) {
cout<<"[Node::Sort] Exchanging Index ["<<i<<"] with Index ["<<i+gap<<"]..."<<endl;
exchange(Student[i], Student[i+gap]);
passOK = false;
}
}
}
if (passOK) {
gap /= 2;
}
}
}
strcmp() expects to receive a character array to do the comparison, but since I am using strings, I cannot do that. What is an alternative? The variable 'lname' needs to be compared and should return true if Student[i].get_lname() is greater than Student[i+gap].get_lname(). The exchange function will then be called and exchange the values of the object's local variables. The objects should be sorted in ascending order based on the value of the 'lname' variable and the 'fname' variable should only be referenced if the two 'lname's being compared are the same.

Answer 1

C++ strings provide implementations of operators < and >, so you can use them instead of strcmp:
std::string a = "hello";
std::string b = "world";
if (a < b) {
cout << a << " is less than " << b << endl;
}