Parsing a string

◀ Random Number Generator▶ Conversion Between char* and string Amazon This function has been covered in-depth by Chapter 12.8, but in case you miss it, let me introduce to you this useful function again. If you have information stored in one single string, separated by a delimiter, you can write a function to parse the string and retrieve relevant data. For example, you can have the following string representing a person’s bank account information, with # being the delimiter:

“0000#7/29/1971#CD#chris@yahoo.com#Amr#99999.99#”

The first substring is the person’s id; the second one is the person’s birthday; the third one is the person’s account type; the fourth one is the person’s email address; the fifth one is the person’s login password; the sixth one is the person’s current balance.

I want to write a function that takes as arguments a string, like the one in the above example, and an index (starting at 1, not 0), specifying which substring to return. The delimiter the function uses is #. The function returns a string which is the substring specified by the index. Now you can start writing this function on your own as an exercise. Here is my version:

#include<iostream>
using namespace std;
#include<string>  /* or <string.h> */

string parse(string s, int i) {
	string t="";
	int counter=0;
	bool start=false;

	for(int j=0;j<s.length();j++) {
		if(s[j]=='#')
			counter++;
		if(!start&&counter==i-1)
			start=true;
		if(counter==i)
			break;
		if(start&&s[j]!='#')
			t+=s[j];
	}
        return t;
}

However, if you know C++ string class very well, you probably know you can take advantage of some of the functions it provides such as find(). Here is another version of the function that utilizes C++ string functions:

#include<iostream>
using namespace std;
#include<string> 	/* or <string.h> */

string parse(string s, int i) {
	if(i<1) return "";
	int d, second, first, pos;

	pos=first=0;
	for(d=0;d<i-1;d++) {
		first=s.find('#',pos);
		if(first==string::npos)
			return "";
		pos=first+1;
	}
	second=s.find('#',pos);
	if(first==0)
		first=-1;
	return s.substr(first+1,second-first-1);
}

◀ Random Number Generator▶ Conversion Between char* and string