How to extract multiple numbers from string in C

Question

I have a question. If I want to extract more than one float number in a string what should I do ? I know that there are functions like strtof by which I can extract the number. The question is what if there are more than one number existing in string ?

I just want and I know that only thing that is needed is pointer to the next character after finding the number. Then continue searching until it reaches \\n but how?

EXAMPLE:

Imagine I have a report about rainfall of some towns during a year and I want to extract rainfall for each town (when it gets to the \\n report for the town is finished ).

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{
    char* data = "Rome:Jan 81.2,Feb 63.2,Mar 70.3,Apr 55.7,May 53.0,Jun 36.4,Jul 17.5,Aug 27.5,Sep 60.9,Oct 117.7,Nov 111.0,Dec 97.9\n"
    "London:Jan 48.0,Feb 38.9,Mar 39.9,Apr 42.2,May 47.3,Jun 52.1,Jul 59.5,Aug 57.2,Sep 55.4,Oct 62.0,Nov 59.0,Dec 52.9\n"
    "Paris:Jan 182.3,Feb 120.6,Mar 158.1,Apr 204.9,May 323.1,Jun 300.5,Jul 236.8,Aug 192.9,Sep 66.3,Oct 63.3,Nov 83.2,Dec 154.7\n"
    "NY:Jan 108.7,Feb 101.8,Mar 131.9,Apr 93.5,May 98.8,Jun 93.6,Jul 102.2,Aug 131.8,Sep 92.0,Oct 82.3,Nov 107.8,Dec 94.2\n"
    "Vancouver:Jan 145.7,Feb 121.4,Mar 102.3,Apr 69.2,May 55.8,Jun 47.1,Jul 31.3,Aug 37.0,Sep 59.6,Oct 116.3,Nov 154.6,Dec 171.5\n"
    "Sydney:Jan 103.4,Feb 111.0,Mar 131.3,Apr 129.7,May 123.0,Jun 129.2,Jul 102.8,Aug 80.3,Sep 69.3,Oct 82.6,Nov 81.4,Dec 78.2\n"
    "Bangkok:Jan 10.6,Feb 28.2,Mar 30.7,Apr 71.8,May 189.4,Jun 151.7,Jul 158.2,Aug 187.0,Sep 319.9,Oct 230.8,Nov 57.3,Dec 9.4\n"
    "Tokyo:Jan 49.9,Feb 71.5,Mar 106.4,Apr 129.2,May 144.0,Jun 176.0,Jul 135.6,Aug 148.5,Sep 216.4,Oct 194.1,Nov 95.6,Dec 54.4\n"
    "Beijing:Jan 3.9,Feb 4.7,Mar 8.2,Apr 18.4,May 33.0,Jun 78.1,Jul 224.3,Aug 170.0,Sep 58.4,Oct 18.0,Nov 9.3,Dec 2.7\n"
    "Lima:Jan 1.2,Feb 0.9,Mar 0.7,Apr 0.4,May 0.6,Jun 1.8,Jul 4.4,Aug 3.1,Sep 3.3,Oct 1.7,Nov 0.5,Dec 0.7";
    const char* towns[14] = {"Rome", "London", "Paris", "NY", "Vancouver", "Sydney", "Bangkok", "Tokyo",
                            "Beijing", "Lima", "Montevideo", "Caracas", "Madrid", "Berlin"};
    size_t i = 0;
    float nums[12];
    char *ch_ptr = strstr(data,towns[0]); //pointing to first character
    const char *stop ="\n";
    while((ch_ptr++) != stop)
        {
            nums[i] = strtof(); ///How should I do it ????
            i++;  
            }   
    return 0;
}

Answer 1

Using two nested for loops, the float value for each town and month can be captured.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{


    char* data = "Rome:Jan 81.2,Feb 63.2,Mar 70.3,Apr 55.7,May 53.0,Jun 36.4,Jul 17.5,Aug 27.5,Sep 60.9,Oct 117.7,Nov 111.0,Dec 97.9\n"
    "London:Jan 48.0,Feb 38.9,Mar 39.9,Apr 42.2,May 47.3,Jun 52.1,Jul 59.5,Aug 57.2,Sep 55.4,Oct 62.0,Nov 59.0,Dec 52.9\n"
    "Paris:Jan 182.3,Feb 120.6,Mar 158.1,Apr 204.9,May 323.1,Jun 300.5,Jul 236.8,Aug 192.9,Sep 66.3,Oct 63.3,Nov 83.2,Dec 154.7\n"
    "NY:Jan 108.7,Feb 101.8,Mar 131.9,Apr 93.5,May 98.8,Jun 93.6,Jul 102.2,Aug 131.8,Sep 92.0,Oct 82.3,Nov 107.8,Dec 94.2\n"
    "Vancouver:Jan 145.7,Feb 121.4,Mar 102.3,Apr 69.2,May 55.8,Jun 47.1,Jul 31.3,Aug 37.0,Sep 59.6,Oct 116.3,Nov 154.6,Dec 171.5\n"
    "Sydney:Jan 103.4,Feb 111.0,Mar 131.3,Apr 129.7,May 123.0,Jun 129.2,Jul 102.8,Aug 80.3,Sep 69.3,Oct 82.6,Nov 81.4,Dec 78.2\n"
    "Bangkok:Jan 10.6,Feb 28.2,Mar 30.7,Apr 71.8,May 189.4,Jun 151.7,Jul 158.2,Aug 187.0,Sep 319.9,Oct 230.8,Nov 57.3,Dec 9.4\n"
    "Tokyo:Jan 49.9,Feb 71.5,Mar 106.4,Apr 129.2,May 144.0,Jun 176.0,Jul 135.6,Aug 148.5,Sep 216.4,Oct 194.1,Nov 95.6,Dec 54.4\n"
    "Beijing:Jan 3.9,Feb 4.7,Mar 8.2,Apr 18.4,May 33.0,Jun 78.1,Jul 224.3,Aug 170.0,Sep 58.4,Oct 18.0,Nov 9.3,Dec 2.7\n"
    "Lima:Jan 1.2,Feb 0.9,Mar 0.7,Apr 0.4,May 0.6,Jun 1.8,Jul 4.4,Aug 3.1,Sep 3.3,Oct 1.7,Nov 0.5,Dec 0.7";
    const char* months[12] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun"
    , "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
    const char* towns[14] = {"Rome", "London", "Paris", "NY", "Vancouver", "Sydney", "Bangkok", "Tokyo",
    "Beijing", "Lima", "Montevideo", "Caracas", "Madrid", "Berlin"};
    size_t i = 0;
    float nums[12];
    char *end = NULL;
    char *town_ptr = NULL;
    char *month_ptr = NULL;
    char monthid[100] = "";
    char townid[100] = "";
    for ( int town = 0; town < 14; town++)
    {
        if ( ( town_ptr = strstr ( data, towns[town]))) {
            i = 0;
            sscanf ( town_ptr, "%99[^:]", townid);
            for ( int month = 0; month < 12; month++)
            {
                if ( ( month_ptr = strstr ( town_ptr, months[month]))) {
                    sscanf ( month_ptr, "%99s", monthid);
                    month_ptr += strlen ( months[month]);
                    nums[i] = strtof( month_ptr, &end);
                    if ( *end == ',' || *end == '\n' || *end == '\0') {
                        printf ( "%s %s nums[%d] = %f\n", townid, monthid, i, nums[i]);
                        i++;
                    }
                }
            }
        }
    }
    return 0;
}

To parse from the town name to a newline. If a month was missing from a town, the previous code would use the month from the next town. This will iterate from the town name until twelve values, a newline, a '\\0' or failure to parse a double.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{


    char* data = "Rome:Jan 81.2,Feb 63.2,Mar 70.3,Apr 55.7,May 53.0,Jun 36.4,Jul 17.5,Aug 27.5,Sep 60.9,Oct 117.7,Nov 111.0,Dec 97.9\n"
    "London:Jan 48.0,Feb 38.9,Mar 39.9,Apr 42.2,May 47.3,Jun 52.1,Jul 59.5,Aug 57.2,Sep 55.4,Oct 62.0,Nov 59.0,Dec 52.9\n"
    "Paris:Jan 182.3,Feb 120.6,Mar 158.1,Apr 204.9,May 323.1,Jun 300.5,Jul 236.8,Aug 192.9,Sep 66.3,Oct 63.3,Nov 83.2,Dec 154.7\n"
    "NY:Jan 108.7,Feb 101.8,Mar 131.9,Apr 93.5,May 98.8,Jun 93.6,Jul 102.2,Aug 131.8,Sep 92.0,Oct 82.3,Nov 107.8,Dec 94.2\n"
    "Vancouver:Jan 145.7,Feb 121.4,Mar 102.3,Apr 69.2,May 55.8,Jun 47.1,Jul 31.3,Aug 37.0,Sep 59.6,Oct 116.3,Nov 154.6,Dec 171.5\n"
    "Sydney:Jan 103.4,Feb 111.0,Mar 131.3,Apr 129.7,May 123.0,Jun 129.2,Jul 102.8,Aug 80.3,Sep 69.3,Oct 82.6,Nov 81.4,Dec 78.2\n"
    "Bangkok:Jan 10.6,Feb 28.2,Mar 30.7,Apr 71.8,May 189.4,Jun 151.7,Jul 158.2,Aug 187.0,Sep 319.9,Oct 230.8,Nov 57.3,Dec 9.4\n"
    "Tokyo:Jan 49.9,Feb 71.5,Mar 106.4,Apr 129.2,May 144.0,Jun 176.0,Jul 135.6,Aug 148.5,Sep 216.4,Oct 194.1,Nov 95.6,Dec 54.4\n"
    "Beijing:Jan 3.9,Feb 4.7,Mar 8.2,Apr 18.4,May 33.0,Jun 78.1,Jul 224.3,Aug 170.0,Sep 58.4,Oct 18.0,Nov 9.3,Dec 2.7\n"
    "Lima:Jan 1.2,Feb 0.9,Mar 0.7,Apr 0.4,May 0.6,Jun 1.8,Jul 4.4,Aug 3.1,Sep 3.3,Oct 1.7,Nov 0.5,Dec 0.7";
    const char* towns[14] = {"Rome", "London", "Paris", "NY", "Vancouver", "Sydney", "Bangkok", "Tokyo",
    "Beijing", "Lima", "Montevideo", "Caracas", "Madrid", "Berlin"};
    float nums[12];
    char *end = NULL;
    char *town_ptr = NULL;
    char monthid[100] = "";
    char townid[100] = "";
    int span = 0;
    for ( int town = 0; town < 14; town++)
    {
        if ( ( town_ptr = strstr ( data, towns[town]))) {//find the town name
            sscanf ( town_ptr, "%99[^:]:%n", townid, &span);
            int each = 0;
            town_ptr += span;
            do {
                sscanf ( town_ptr, "%s%n", monthid, &span);
                town_ptr += span;
                nums[each] = strtod ( town_ptr, &end);
                if ( end == town_ptr) {//failed to parse a double
                    break;
                }
                printf ( "%s %s nums[%d] = %f\n", townid, monthid, each, nums[each]);
                town_ptr = end + 1;//to advance past the comma
                each++;
            } while ( each < 12 && *end != '\0' && *end != '\n');
        }
    }
    return 0;
}