Code Parsing in C/C++

Hi Guys,

I am looking for a solution of parsing data in C language, I have attached the code below with some comments in it. What actually I am looking for not to call the sscanf function with the number data is available (In this it is 3) as it is random and can be anywhere between 0 to 9.

Code:

---

main()
{
    char buffer[500] = "DATA:  3,43,56,32f402,44,57,32f403,45,58,32f404";
    char *buf = buffer;
    int count;
    sscanf(buffer, "DATA: %d", &count); //First Value is Count, get it in a variable.
    printf("Count - %d\n", count);
    buf+=8; //strlen("DATA: 3,") = 8
    for(int c = 0; c < count; c++)
    {
        int a1, a2, a3;
        sscanf(buf, "%d,%d,%x", &a1, &a2, &a3);
        printf("%d,%d,%x\n", a1, a2, a3);
        buf+=13;//strlen("43,56,32f402,");
    }
    return 0;
}

---

Can some one suggest any alternate solution with less number of calls to sscanf, in this sample code it is happenning count+1 times.

If anyone can point me to C++ library routine will be helpfull as well.

Many thanx,
Sgies

First main returns int.
And the solution to this would probably be to search for , and then extract. This could be done in various ways. For example, strstr to search for a , and then truncate that with a \0 and use appropriate library function such as strtol to convert the buffer to an integer.
Then you could use a pointer to set the next position in the buffer and continue this approach:

Code:

---

const char* buf = "This,is,a,test";
const char* p = buf;
while (p < buf + strlen(buf))
{
        char* pPos = strstr(p, ",");
        *pPos = '\0';
        long mylong = strtol(buf, NULL, 10);
        p = pPos + 1;
}

---

Something like that. Not tested, of course.

2Elysia - strchr will be better than strstr
strtol requires 3 parameters the pointer to the end of parsed number and base which should be 10 or 16 depending on the position of the number in string

2sgies - %n in scanf will give the position where the parsing stopped
It could be used to avoid magic constants like += 8 and += 13

Quote:

---

Originally Posted by vart

2Elysia - strchr will be better than strstr
strtol requires 3 parameters the pointer to the end of parsed number and base which should be 10 or 16 depending on the position of the number in string

---

I'm not very familiar with C functions, and I've never used strchr so you'll forgive me for not giving out 100% perfect code.
Oh yes, I always forget that strtol takes 3 arguments. Let me fix that...

You can use strtok() to chop up the data, especially if your delimiters are no more complicated that a single comma.

If your C library is POSIX, you can use regex.h functions to parse it (but then you've got two problems).

Or you could go to the extreme and learn about lex.

Thanks guys for your answers but I like to concentrate on sscanf rather then using strchr or strtok. If you can please turn back the topic on discussing sscanf will be great.

BTW 3 in the sample code I mention can be seen as 3 rows (with 3 elements in each which I am parsing in loop) in case I am not clear in writing.

Sgies

You could use a pointer to specify the position in the file for sscanf to start extracting. But you will still need to find the next ",", so using a searching function might still be necessary.

Quote:

---

Originally Posted by Elysia

You could use a pointer to specify the position in the file for sscanf to start extracting. But you will still need to find the next ",", so using a searching function might still be necessary.

---

Using %n format you can also know where the sscanf stopped parsing and continue parsing from that position

This code works:

Code:

---

#include <stdio.h>

int main()
{
    char buffer[500] = "DATA:  3,43,56,32f402,44,57,32f403,45,58,32f404";
    char *buf = buffer;
    int count;
        int pos;
    sscanf(buffer, "DATA: %d,%n", &count,&pos); //First Value is Count, get it in a variable.
    printf("Count - %d\n", count);
    buf+=pos; //strlen("DATA: 3,") = 8
    for(int c = 0; c < count; c++)
    {
        int a1, a2, a3;
        sscanf(buf, "%d,%d,%x,%n", &a1, &a2, &a3, &pos);
        printf("%d,%d,%x,%d\n", a1, a2, a3, pos);
        buf+=pos;
    }
    return 0;
}

---

As does this, but it's certainly a bit more complicated:

Code:

---

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

void bad_input()
{
        printf("could not parse input\n");
        exit(1);
}

int main()
{
        char buffer[500] = "DATA:  3,43,56,32f402,44,57,32f403,45,58,32f404";
        char *buf = buffer;
        int count;
        int pos;
        char *p;
        char *after;
        p = strchr(buf, ':');
        if (!p) bad_input();
        buf = p+1;
        count = strtol(buf, &after, 10);
        printf("Count - %d\n", count);
        buf = after+1;
        for(int c = 0; c < count; c++)
        {
                int a1, a2, a3;
                assert(*after == ',');
                a1 = strtol(buf, &after, 10);
                buf = after+1;
                assert(*after == ',');
                a2 = strtol(buf, &after, 10);
                buf = after+1;
                assert(*after == ',');
                a3 = strtol(buf, &after, 16);
                buf = after+1;
              printf("%d,%d,%x\n", a1, a2, a3);
        }

        return 0;
}

---

Ok, so the latter code does some more error checks, which could help if the input data is "malformed" for any reason.

--
Mats