Modify String Data

Question

I want to substring and modify my string (which is defined below).

char gps[]="$GPGGA,115726.562,4512.9580,N,03033.0412,E,1,09,0,9,300,M,0,M,,*6E";

Shortly, I want to take and increase Lat,Long data which means

My steps

Take lat info as char or float
Convert lat(char) to float
Add step value to float
Convert lat(float) to char as newlat
Insert newlat into gps[]
printf

  char substr[10];  //4512.9580 //#number of char
  memcpy(substr,&gps[19],10); //memcpy from gps char start from 19 take 9 char character
  substr[10]='\0';  //I dont know what makes it
  char lat[10]=???  //I dont know how I will take lat data
  float x;      //defined float value
  x=atof(lat);      //convert string to float
  x=x+0.1;      //add step value to float (4513.0580)
  char newlat[10];  //newlat defined
  sprintf(newlat,x);    //convert to float to string
  ????          //I dont know how I can put into gps[]

So you want to copy nine characters into a nine-character array, and then terminate it *where*? At position ten, which is outside the array? — Some programmer dude, Jul 23 '14 at 08:07
Regarding your floating point manipulation, you might want to read [What Every Computer Scientist Should Know About Floating-Point Arithmetic](http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html), because the result will probably not be what you expect it to be. — Some programmer dude, Jul 23 '14 at 08:09
Would you want to use `double` for precision is good. accuracy is not enough, perhaps in `float`. — BLUEPIXY, Jul 23 '14 at 08:15
Dear Joachim,If I understand correctly, lat(first lat data(not changed)), newlat(changed lat data should be inserted gps[]) — user3722613, Jul 23 '14 at 08:15
I am using CCS C, "not a supported data type" for double from user manual — user3722613, Jul 23 '14 at 08:17
I'm telling you that you need a ten character array to store a nine-character text. — Some programmer dude, Jul 23 '14 at 08:28
@JoachimPileborg I think that It should seek length as a comma-separated it. — BLUEPIXY, Jul 23 '14 at 08:33
It is not possible to write back if the result number of digits of addition is increased. — BLUEPIXY, Jul 23 '14 at 08:53

Abend · Answer 1 · 2014-07-23T10:33:40.393

0

Try this:

char substr[10];
float x;

memcpy(substr,&gps[18],9);
substr[9]='\0';
x=atof(substr);
x=x+0.1;
sprintf(substr,"%.4f",x);
memcpy(&gps[18];substr,9);

edited Jul 23 '14 at 10:33

answered Jul 23 '14 at 09:00

Abend

589
4
14

Thank you for your work. it works excellent with adding #include library and changing memcpy(&gps[18],substr,9); – user3722613 Jul 23 '14 at 14:45

BLUEPIXY · Answer 2 · 2014-07-23T09:40:15.813

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

int add(char *x, const char *dx){
//Note that this is not a general-purpose
    int ppos1 = strchr(x, '.') - x;
    int ppos2 = strchr(dx, '.') - dx;
    int len2 = strlen(dx);
    //4512.9580
    //+  0.1
    int i = len2 -1;//dx's last char
    int j = ppos1 + (i-ppos2);//x's add position
    int carry = 0;
    for(;i>=0 || (j>=0 && carry);--i, --j){
        if(dx[i]=='.')
            continue;
        int sum = (x[j]-'0')+(i>=0)*(dx[i]-'0')+carry;
        x[j] = sum % 10 + '0';
        carry = sum / 10;
    }
    return carry;
}

int main(){
    char gps[]="$GPGGA,115726.562,4512.9580,N,03033.0412,E,1,09,0,9,300,M,0,M,,*6E $GPRMC,115726.750,A,4002.9675,N,03233.0412,E,173.8,0,071114,003.1,E*72";  int m,k,j,i,n;
    char *field, *rest;
    field = strchr(gps, ',');//1st ','
    field = strchr(field+1, ',')+1;//2nd ',' next(+1) : 3rd field
    rest = strchr(field, ',');//3rd ','
    int substr_len = rest - field;
    char substring[substr_len + 1];
    memcpy(substring, field, substr_len);
    substring[substr_len] = '\0';
    if(add(substring, "0.1")){//Carry occurred
        char newgps[sizeof(gps)+1];
        *field = '\0';
        strcpy(newgps, gps);
        strcat(newgps, "1");
        strcat(newgps, substring);
        strcat(newgps, rest);
        printf("%s\n", newgps);
    } else {
        memcpy(field, substring, substr_len);//rewrite
        printf("%s\n", gps);
    }
    return 0;
}

Modify String Data

2 Answers2