using stringstream to conver string to int - c++

Question

this is my function
void global::readData(lifeform &p)
{
std::ifstream ifs("data.txt");
int i=0,i_str=0;
std::string str,str2;
std::getline(ifs,str);
std::stringstream ss(str);
if(i<31) {
std::getline(ss,str2,',');
std::istringstream toint(str2);
toint >> i_str;
if(i_str ==1) { //here i_str can get 1
p.newgame=1;
while(i<31) {
std::getline(ss,str2,',');
toint >> i_str;
if(i==0) {
p.setName(str2); //this also works
}
if(i==1) {
p.setMaxHp(i_str); //doesnt work
}
if(i==2) {
p.setQName("main",str2); //works
}
i++;
//....
}
}
this is data.txt
1,furkan,100,No mission,
i tried to get what is written on the data.txt to str.there is no problem so far.after than i wanted to convert string to int it worked in the first converting but not the rest
i changed 1 to 0 to see if it works or not and it works but the rest i_str doesnt work

Answer 1

1) std::istringstream get his own copy of str2. It don't watch changes of this variable.
2) And how you should do it:
char c;
ss>>i_str//read int value from stream
>>c;//and throw away separator
You don't need getline here.

Answer 2

Warning: this answer is kind of overkill for the specific job at hand. It uses a couple of fairly general-purpose utilities that make the job easy, but probably would be worth writing if this was the only time/place you had a use for them (but it's not--they turn out to be quite useful in general, once you have them). I keep them in an "input_utils.h", where I can use them from almost anything quite easily.
The first is an input operator for a constant string. That may sound utterly pointless (if it's constant, you obviously can't read into it). What it does is read some fixed input from a stream, and verify that what was in the stream matches what you expected. The code looks like this:
std::istream &operator>>(std::istream &is, char const *label) {
if (is.flags() & std::ios::skipws)
while (std::isspace((unsigned char)is.peek()))
is.ignore(1);
while (is.peek() == *label) {
is.ignore(1);
++label;
}
if (*label)
is.setstate(std::ios::failbit);
return is;
}
This lets us read (most of) the commas in your input quite easily--verify that they're present, but otherwise ignore them. So, to read three numbers separated by commas, we would do something like this:
input_stream >> number1 >> "," >> number2 >> "," >> number3;
At least to me, the meaning seems pretty simple, straightforward and obvious (and the applicability to the job at hand seems almost equally obvious).
The second has a clear and obvious intent, but the implementation is a little less trivial than I'd like (but I don't know a way to make it any simpler and still do the job). Its code looks like this:
class line_proxy {
std::string &s;
char delim;
public:
line_proxy(std::string &s, char delim) : s(s), delim(delim) {}
friend std::istream &operator>>(std::istream &is, line_proxy const &p) {
std::getline(is, p.s, p.delim);
return is;
}
};
line_proxy line(std::string &in, char delim = '\n') {
return line_proxy(in, delim);
}
We use it like this:
std::string s;
input_stream >> line(s); // equivalent to `std::getline(input_stream, s);`
Again, even though the implementation is a bit on the complex side, the use seems pretty obvious (at least to me).
Once we have these, your job borders on trivial. The one part that I'd do that might initially seem a little on the tricky side would be implementing the reading in a stream extraction operator for the lifeform class:
#include "input_utils.h"
struct lifeform {
int index;
std::string name;
int level;
std::string mission;
friend std::istream &operator>>(std::istream &is, lifeform &f) {
return is >> f.index
>> ","
>> line(f.name, ',')
>> f.level
>> ","
>> line(f.mission, ',');
}
We might want to be able to write out a lifeform as well:
friend std::ostream &operator<<(std::ostream &os, lifeform const&f) {
return os << "Index: " << f.index
<< ", name: " << f.name
<< ", level: " << f.level
<< ", mission: " << f.mission;
}
...and a little code to test them and see that they work correctly:
int main() {
std::istringstream input("1,furkan,100,No mission,");
lifeform f;
input >> f;
std::cout << f;
}