C: Extracting part of a string

trevorv · 08-29-2007, 11:45 AM

After a couple of weeks break due to other commitments, I've started learning C again. I'm writing a simple address book program. In order to know what types of data to ask for the program reads a config file containing the data, e.g.

Code:

field.firstname "First name"
field.surname "Surname"
field.jabber "Jabber ID"

I have written the part which reads this file, it takes a line at a time. I cannot figure out, however, how I can extract the part of the newly read string between quotation marks.

In other words, I want to give the part of each line in quotation marks to printf, but I don't know how to separate it from the rest.

Help appreciated :-)

tsv

rjwilmsi · 08-29-2007, 12:41 PM

One way would be to do a character by character compare on the whole string and cat characters after the first " and before the second " into a new string:

Code:

for (i = 0; i < strlen(inputstring); i++)
{

if (start_cat == 0  && inputstring[i] == '"') // start of string
  start_cat = 1;
else if (inputstring[i] == '"') // end of string
   start_cat = 0 ;
else if (start_cat == 1) // in the string
 strcat(outputstring, inputstring[i]);

}

probably ugly but something like that will work

Wim Sturkenboom · 08-29-2007, 03:17 PM

Not tested:

Code:

ptr1=strchr(thestring,"\""); // find first double quote
ptr1++;
ptr2=strchrt(ptr1,"\""); // find second double quote
*ptr2='\0';
printf("%s\n",ptr1);
*ptr2="\""; // restore original value (if necessary)

Not included is error checking if the quotes are actually found.

henk1420 · 08-29-2007, 04:36 PM

G'day,

You may use the function strtok.

char *token_, *your_string;

if ( (token_ = strtok(your_string, "\"\r\n")) == NULL)
{
// do some error messages and return
}

// token_ now contains the first part: with the . inside

if ( (token_ = strtok(NULL, "\"\r\n")) == NULL)
{
// do some error messages and return
}

// token_ points to the string between the double quotation marks
// just where you were looking for.

In stead of using strtok, which mangles your_string, you can use strsep instead. It does not mangle your string.

Both functions require to include <string.h>

Regards,
H