如何从字符串中提取数字字段？

Question

The problem I face is the follows:

I have a string which contains information which is in the following fixed information.

club {
level: 210
league: 128
staff: 1451
salary: 3452600
}
club {
level: 211
league: 121
staff: 1451
salary: 3452600
}
... and many more club {...}

I have many entries of club . I want to be able to just extract all the numbers from ALL of the club in a string in the following format.

Desired Output:

2101281451345260021112114513452600

I have the information in the string but I am not able to understand how to efficiently remove the repeating fields from the string such as level:, league:, staff:, club:, salary:, club {} .

I would appreciate any help for a simple algorithm which achieves this.

Answer 1

You don't need to treat your numbers as numbers, treating them as characters is good enough.

To check whether a character is a digit, use isdigit :

str = ...;
for (char c: str)
    if (isdigit(c))
        std::cout << c;

Answer 2

You could make use of the erase-remove idiom :

#include <algorithm>
#include <string>
#include <cctype>

int main()
{
    std::string input = "club {"\
        "level: 210"\
        "league : 128"\
        "staff : 1451"\
        "salary : 3452600"\
        "}";

    input.erase(std::remove_if(input.begin(), input.end(), [](char c) { return !std::isdigit(c); }),
        input.end());
    //string is now "21012814513452600"
    return 0;
}

This will remove all non-digits from your string.

Answer 3

One idea to extract numbers as numbers: you can replace all unneeded characters by spaces, then get the numbers from the string using stringstream :

std::string str = ...;
std::string temp = str; // avoid overwriting the original string
for (char& c: temp) // '&' gives you permission to change characters
    if (!isdigit(c))
        c = ' ';
std::stringstream stream(tmp);
int i;
while (stream >> i)
    std::cout << i; // print it or do whatever else