Key-Value pair in C?

Question

I have a string in the format of

"SERVERID=12345\nSERVERKEY=asdasw\nSERVERAPPID=123213\n"

I've parsed this line by line using strtok(). Is there a way to make a key-value pair of each line? Like maybe store them in some sort of an array? What I mean is, if I want SERVERID, I just say Array['SERVERID'] and it'll return 12345 as the value. Is there a way to do it in C?

There are (non-standard) ways to achieve more or less the result, but not using the notation you suggest. The string should be in double quotes, and you'd need to use a function call to do the lookup, and you'd use a structure behind the scenes, and you'd have other functions to create the array of key-value pairs, and to add key-value pairs, and to remove them, and so on. It would be done using functions all the way around. — Jonathan Leffler, Jul 03 '18 at 05:06
You need to write your own data structure for that in C. If you can write it in C++ i would use that and use a map that's built in — , Jul 03 '18 at 05:08
@JonathanLeffler Is there an example code of such an implementation? — Shantanu Mhapankar, Jul 03 '18 at 05:10
I'm thinking of the code in "C Interfaces and Implementations: Techniques for Creating Reusable Software" by D R Hanson (Addison-Wesley Professional Computing Series, 1997, ISBN 0-201-49841-3). Source etc available from GitHub (https://github.com/drh/cii). — Jonathan Leffler, Jul 03 '18 at 05:16
Depending on your implementation, your could try the functions `hsearch` or `lsearch`. They are not standard C but exist on most posix systems. — Serge Ballesta, Jul 03 '18 at 05:26

score 3 · Answer 1 · answered Jul 03 '18 at 09:07

Standard C doesn't give you any "container types" like the one you're looking for. Still you have several options to solve your problem:

Might sound silly, but you could switch to a different language. It's at least something to think about. For example, C++ comes to mind, offering the std::map type.
Use some third-party library. A popular choice is GLib, it offers a hash table you could use.

There's always the option to implement it yourself. A very simple idea would be to use an array of a struct, e.g.

struct stringpair {
    char *key;
    char *value;
};

struct stringpair *table;

// ...
size_t entries = 42; // number of entries you found
table = malloc(entries * sizeof *table); // check for NULL after this

// look for an entry:
char *value = 0;
for (size_t i = 0; i < entries; ++i)
{
    if (!strcmp(table[i].key, "SERVERID"))
    {
        value = table[i].value;
        break;
    }
}

This is of course a very basic solution and doesn't perform well with a lot of entries. I also didn't test this code, it's just to give you a rough idea. If you need fast lookups, you will need to implement a hashtable instead, or use option 1 or 2.

score 0 · Answer 2 · answered Jul 03 '18 at 05:06

0

What you're looking for here would be a form of a dictionary. Typically, but not always, these use hashtables. There are many ways of creating a hashtable in C

You can find your answer here: What is a hash table and how do you make it in C?

You could also see other implementations such as a combined data structures, like a dictionary-linked list, and more. Just find a way to convert your string (char *) into a number, and find a way to use that number as an index.

answered Jul 03 '18 at 05:06

Nova Ardent

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This looks more as a comment instead of answer. – unalignedmemoryaccess Jul 03 '18 at 06:47
I don't have commenting privileges yet, but would have liked to answer this question anyways. Do you recommend I delete it? if so, could I have a further explanation as not to make the same mistake down the road? – Nova Ardent Jul 03 '18 at 06:49
I'd say it's not a good answer, still the link and short explanation could be helpful, so, it's not a *bad* one either -> keep it. – Jul 03 '18 at 09:31

Key-Value pair in C?

2 Answers2