kv_get_value.c

Simple ANSI C Key Value String Parser

Writeup about this mini project https://briankhuu.com/blog/2025/01/30/simple-key-value-text-parser-in-c/

If you need a kv parser that can be more easily modified. Consider https://github.com/mofosyne/kv_parse.c

Get Value

This function searches for a specified key in a formatted key-value string and extracts its corresponding value into the provided buffer.

Pros:

• Self contained. Only stdio.h required for kv_file_get_value()
• Minimise Size
• Minimise Complexity

Cons:

• Scan entire file for one key. This gets very inefficient for larger KV files. But practically very fast for small projects.
• Not easy to parse INI file, you would need to read an INI section into it's own buffer then pass it to this function

unsigned int kv_get_value(const char *str, const char *key, char *value, unsigned int value_max);
unsigned int kv_file_get_value(FILE *file, const char *key, char *value, unsigned int value_max);

This above will be able to read Bash Style key value files

XDG_SESSION_DESKTOP=cinnamon
QT_QPA_PLATFORMTHEME=qt5ct
XDG_SESSION_TYPE=x11

But we can also interpret ':' and also skip whitespace. (Disable via KV_PARSE_DISABLE_WHITESPACE_SKIP compile flag).

XDG_SESSION_DESKTOP   : cinnamon
QT_QPA_PLATFORMTHEME  : qt5ct
XDG_SESSION_TYPE      : x11

You can also escaped quote strings like in c (Disable via KV_PARSE_DISABLE_QUOTED_STRINGS compile flag).

XDG_SESSION_DESKTOP="cinnamon"
QT_QPA_PLATFORMTHEME="qt5ct"
XDG_SESSION_TYPE="x11"

Supported Features:

• Whitespace Skipping (Disable via: KV_PARSE_DISABLE_WHITESPACE_SKIP): Ignores spaces and tabs around keys and values.
• Quoted String Support (Disable via: KV_PARSE_DISABLE_QUOTED_STRINGS): Handles values enclosed in single (') or double (") quotes.
• Key Delimiters : Supports both = and : as key-value separators.

Usage Example:

kv_get_value()

char buffer[50];
unsigned int len = kv_get_value("username=admin\npassword=1234", "username", buffer, sizeof(buffer));
if (len > 0) {
    printf("Username: %s\n", buffer);
} else {
    printf("Key not found.\n");
}

kv_file_get_value()

char buffer[50];
FILE *temp = tmpfile();
fputs("username=admin\npassword=1234", temp);
rewind(temp);
unsigned int len = kv_file_get_value(temp, "username", buffer, sizeof(buffer));
if (len > 0) {
    printf("Username: %s\n", buffer);
} else {
    printf("Key not found.\n");
}