Sum all integers in a string C++ - c++

Question

I have a C++ string in my code that is like:
"1 2 3 4 5 6 7 8"
I know the string is composed of integers separated by a space char. How can I sum them?
I'm quite a C++ newbie and in Java I'd simply do:
String str = "1 2 3 4 5 6 7 8";
int sum = 0;
for (int i = 0; i < str.split(" ").length; i++ {
sum += Integer.parse(str.split(" ")[i];
}
How can I do just like this with my string object in C++?
Some people suggested me stringstream but I still can't understand this object and I need to read the string entirely, getting every single digit within it.
Thanks in advance!
Update: some guys nicely tried to help me but still it's not working. Perhaps because of some quirk of my problem which I haven't clarified before. So here it goes:
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
freopen("variable-exercise.in", "r", stdin);
int sum = 0, start = 0;
string line;
while(getline(cin ,line)) {
istringstream iss(line);
while(iss >> start) {
sum += start;
}
cout << start << endl;
sum = start = 0;
}
return 0;
}
Ah, the input file contains the following:
1
3 4
8 1 1
7 2 9 3
1 1 1 1 1
0 1 2 5 6 10
So, for each line, the program must print the sum of all integers in the string line. This example would generate:
1
7
10
21
5
24
thanks

Answer 1

Some people suggested me stringstream but I still can't understand this object and I need to read the string entirely
I guess you were given a good advice. With std::istringstream you could just read in values one after the other as you would read them from the standard input (or any other input stream).
For instance:
#include <sstream>
#include <string>
#include <iostream>
int main()
{
// Suppose at some time you have this string...
std::string s = "1 2 3 4 5 6 7 8 9 10";
// You can create an istringstream object from it...
std::istringstream iss(s);
int i = 0;
int sum = 0;
// And read all values one after the other...
while (iss >> i)
{
// ...of course updating the sum each time
sum += i;
}
std::cout << sum;
}

Answer 2

Like this:
std::stringstream s("1 2 3 4 5 6 7 8 9");
int n = 0;
int x;
while (s >> x)
n += x;
std::cout << n << std::endl;
After your edit:
cout << start << endl;
This is wrong, you should be printing sum instead:
cout << sum << endl;

Answer 3

I used C code to solve this problem. Here's the final solution:
#include <stdio.h>
#include <string.h>
int main() {
char *c;
char line[100];
int x, sum = 0;
while(gets(line)) {
for(c = strtok(line, " "); c ; c = strtok(NULL, " ")) {
sscanf(c, "%d", &x);
sum += x;
}
printf("%d\n", sum);
sum = 0;
}
return 0;
}
Hope it helps anyone who might have the same problem!