Extract fields and values from text line using C++ - c++

Question

I am reading in a text file with lines of the format:
date =20170422,line =10,index =3,field =partType,lock =productCode1,bookmark=2/19/56,
I need to extract the name of the field (date, line, index, etc.) and its corresponding value into char field[] and char value[] variables. If necessary, I am allowed to modify the format of the lines.
My initial thinking was to use while loops and check for = and , characters but it was getting messy and it seems like there may be a cleaner way.

Answer 1

You could do something like the below example. Split the string by commas using getline from your file, then split use an istringstream to and getline to split it again by an equals sign.
#include<iostream>
#include<fstream>
#include<string>
#include<sstream>
int main()
{
std::ifstream file("test.txt");
std::string wholeLine, partOfLine;
while(std::getline(file, wholeLine, ',')) {
std::istringstream wholeLineSS(wholeLine);
while(std::getline(wholeLineSS, partOfLine, '=')) {
std::cout<<partOfLine<<std::endl;
}
}
return 0;
}

Answer 2

The program I post here extracts the parameters from one or more strings which are formatted as you require. The function extract extracts all the parameters contained in a string (of the format you specified) and insert their names and values in a structure (struct sParms) array.
You may compile the program as extract and execute it at the system prompt as:
username: ./extract "date =20170422,line =10,index =3,field
=partType,lock =productCode1,bookmark=2/19/56,"
The output will be the following:
[date]=[20170422]
[line]=[10]
[index]=[3]
[field]=[partType]
[lock]=[productCode1]
[bookmark]=[2/19/56]
You may execute the program with more than one string:
username: ./extract "date =20170422,line =10,index =3,field
=partType,lock =productCode1,bookmark=2/19/56," "yes=1, no=0"
The output will be the following:
[date]=[20170422]
[line]=[10]
[index]=[3]
[field]=[partType]
[lock]=[productCode1]
[bookmark]=[2/19/56]
[yes]=[1]
[no]=[0]
In the following line there's the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libgen.h>
//Parameters: date =20170422,line =10,index =3,field =partType,lock =productCode1,bookmark=2/19/56,
#define SEPARATOR ','
#define ASSIGNEMENT '='
typedef struct sParms {
char * fieldName;
char * fieldValue;
} tsParms;
int loadString(char *to, const char *from);
int extract(tsParms **oparms, const char *inb);
// Retrieve buffer length
int loadString(char *to, const char *from)
{
int len=0;
while(*from<=32 && *from!=SEPARATOR && *from!=ASSIGNEMENT)
from++;
// Get the string value
while(*from>32 && *from!=SEPARATOR && *from!=ASSIGNEMENT) {
*(to+len++)=*from;
++from;
}
*(to+len++)=0;
return len;
}
int extract(tsParms ** oparms, const char *inb)
{
int cnt=0,j;
const char * end, *equ, *start;
char * buff;
tsParms * parms;
if (inb == NULL || strlen(inb) == 0 || oparms == NULL)
return 0;
// It counts the number of parms
end=strchr(inb,ASSIGNEMENT);
while(end) {
cnt++;
end=strchr(end+1,ASSIGNEMENT);
}
if (!cnt)
return 0;
/* Doing some considerations we may assume that the memory to use to store
* fields name and values is the same of the input string (inb)
*
* The space to store the pointers is cnt * sizeof(tsParms *).
*/
j=cnt * sizeof(tsParms) + strlen(inb);
parms = malloc(j+1);
memset(parms,0,j+1);
buff = (char *)(parms+cnt); // The memory area where we can save data!
start=inb;end=start;cnt=0;
do {
end=strchr(start,SEPARATOR);
equ=strchr(start,ASSIGNEMENT);
if (equ) {
//Get the field name
parms[cnt].fieldName=buff;
buff+=loadString(buff,start);
//Get the field value
start=equ+1;
parms[cnt].fieldValue=buff;
buff+=loadString(buff,start);
cnt++;
}
if (end)
start=end+1;
} while(end);
*oparms = parms;
return cnt;
}
int main(int argc, char *argv[])
{
int i,j,cnt=0,retval=0;
tsParms * parms=NULL;
if (argc<2) {
printf("Usage: %s \"string-1\" [\"string-2\" ...\"string-n\"]\n",basename(argv[0]));
return 1;
}
for(i=1; i<argc; i++) {
cnt=extract(&parms, argv[i]);
if (cnt!=0 && parms!=NULL) {
for(j=0;j<cnt;j++) {
printf("[%s]=[%s]\n",parms[j].fieldName,parms[j].fieldValue);
}
puts("");
free((void *)parms);
} else {
retval=1;
break;
}
}
return retval;
}