How to print related lines in c++? - c++

Question

In my code, I want to have a function called search that goes through each line in a .txt file and prints out the line if the first number in the sentence contains the number given by the user. For example:
Format of the .txt file:
Each word is separated by a space.
17 35 "door"
40 19 "wall"
17 34 "car"
3 9 "window"
Output:
Enter a desired number:17
17 35 "door"
17 34 "car"
How would I go about doing this? In java, I would normally use the .split() function to split the sentence into a list then see if the first index matches the desired input, but I can't find how to do this, and what I can find, I don't understand. My attempts are listed below, but if you have better methods, please list them...I'm still learning. My attempt are located under the search function below:
#include<iostream>
using std::cerr;
using std::endl;
#include <list>
using namespace std;
#include <fstream>
using std::ofstream;
#include <cstdlib> // for exit function
#include <sstream>
using namespace std;
class Item{
//Access specifer
public: //todo, private with get/set
string item;
int meshNum;
int mNum;
//constructor
public:
Item( string item,int mNum, int meshNum ){
this->item=item;
this-> mNum= mNum;
this-> meshNum= meshNum;
}
//Memeber functions
public:
string getItem(){
return item;
}
void setItem(string item){
this->item = item;
}
int getMeshNum(){
return this->meshNum;
}
void setMeshNum(int meshNum){
this->meshNum= meshNum;
}
int getMNum(){
return this->mNum;
}
void setMNum(int mNum){
this-> mNum= mNum;
}
};
//____________________________________________
class materialList{
// Access specifer
private:
list <Item> items;
//constructor
public:
/* materialList(){
this->items = new list<Item>;
} */
// Memeber fucntions
public:
void add(Item &item)
{
items.push_back(item);
}
//print my list
void Print()
{
ofstream outdata; // outdata is like cin
outdata.open("example2.dat"); // opens the file
if( !outdata ) { // file couldn't be opened
cerr << "Error: file could not be opened" << endl;
exit(1);
}
for (auto &i : items)
outdata << i.getItem() << " "<<i.getMeshNum()<< " "<<i.getMNum()<<endl;
outdata.close();
}
void search(ifstream& inFile){ //this function is where I need help on =<
string line,word;
int materialNum;
istringstream iss;
cout<< "Enter a material number:";
cin>>materialNum;
int**arr= (int**)malloc(20*sizeof(int*));
int i=0;
while(!inFile.eof()){
// read line by line from the file
getline(inFile,line);
if(inFile.good()){
// read word by word in line and place words in arr
iss.clear(); // clear out state
iss.str(line);
iss>> word;
arr[i]=word;
}
if (word==cin){
cout>>line;
}
}
}
};
int main(){
bool value = true;
string objectName;
int Mnum;
int Meshnum;
materialList ml; //(list<Item> test);
while(value){
cout<< "Enter Object name: ";
cin>> objectName;
cout<<" Enter M#: ";
cin>> Mnum;
cout<<"Enter Mesh#: ";
cin>> Meshnum;
//Item second= Item(objectName,Mnum,Meshnum);
ml.add(Item(objectName,Mnum,Meshnum));
ml.Print();
}
//Item test= Item("door",34,50);
//itemList =
//ml.add(test);
//ml.Print();
}
Errors:
material_characterizationf.cpp:105:20: error: assigning to 'int *' from incompatible type 'std::__1::string' (aka 'basic_string<char, char_traits<char>, allocator<char> >')
arr[i]=word;
^~~~
material_characterizationf.cpp:134:17: error: non-const lvalue reference to type 'Item' cannot bind to a temporary of type 'Item'
ml.add(Item(objectName,Mnum,Meshnum));
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I know the first error comes from my failed attempts, but I have no idea where the second error came from. The code was working fine until I tried to add a search function.

Answer 1

In your search function, I don't think you need to use the arr array as not only does it cause memory leak due to it not being freed at the end of the function but also it doesn't serve any purposes in the function. You can simply parse the first argument of the input lines from the file as int type into the word variable by setting the word variable as int type instead of string.
That way you can use word to check if it is equal to the materialNum (not equal to cin in your original code as it is an istream object and can't be compared with an integer) input by the user at line (cin >> materialNum;). If word is equal to materialNum, then you can print out the file line using out << line << ends;.
void search(ifstream& inFile){
string line;
int word;
int materialNum;
istringstream iss;
cout << "Enter a material number:";
cin >> materialNum;
int i=0;
while(!inFile.eof()){
// read line by line from the file
getline(inFile,line);
if(inFile.good()){
// read word by word in line and place words in arr
iss.clear(); // clear out state
iss.str(line);
iss >> word;
}
if (word == materialNum){
cout << line << endl;
}
}
}
Update: If you know the file name, you can create a ifstream object (inFile) to open it, and then pass it as an argument to your search function. For example, you can do something like this in your main function
string filename = "example2.dat";
ifstream inFile;
inFile.open(filename, std::ifstream::in);
ml.search(inFile);