File based Database using Gunzip

• zlib is a software library used for data compression.
• The zlib library provides Deflate compression and decompression code for use by zip, gzip, png (which uses the zlib wrapper on deflate data).
• gzread decompresses as you read it.

Program:

 
/* File based Database using Gunzip
 * Check : http://velrajcoding.blogspot.in
 */

#include <stdio.h>
#include <zlib.h>    // For gunzip

enum {
    TAG_VER = 1,
    TAG_DATA,
};

#define FILE_PATH_TMP     "file_gz_db.gz.tmp"
#define FILE_PATH         "file_gz_db.gz"
#define VERSION_1         1
#define STU_ID            100
#define STU_NAME          "Velraj"
#define STU_TOTAL         500

void save_db()
{
    char buf[256] = {0};
    int  len = 0;
    gzFile gz_file = NULL;

    if (!(gz_file = gzopen(FILE_PATH_TMP, "wb"))) {
        printf("Failed gzopen !");
        return;
    }

    len = snprintf(buf, sizeof(buf), "%d\a%d\n", TAG_VER, VERSION_1);
    if (len != gzwrite(gz_file, buf, len)) {
        printf("Failed to writing db header!");
        goto end;
    }

    len = snprintf(buf, sizeof(buf), "%d\a%d\a%s\a%d\n", TAG_DATA,
                   STU_ID, STU_NAME, STU_TOTAL);
    if (len != gzwrite(gz_file, buf, len)) {
        printf("Failed to writing db header!");
        goto end;
    }
    rename(FILE_PATH_TMP, FILE_PATH);

end:
    gzclose(gz_file);
    return;
}

void read_db()
{
    gzFile gz_file = NULL;
    char   buf[256] = {0}, str_tag[16] = {0}, str_stu_id[12] = {0}, str_name[64] = {0}, str_total[12] = {0};
    int    tag = 0, version = 0, ret = 0;

    if (!(gz_file = gzopen(FILE_PATH, "rb"))) {
        printf("gzopen is failed to open the file");
        return;
    }
    if (gzgets(gz_file, buf, sizeof(buf)) == NULL) {
        printf("File is doesn't have any content");
        goto end;
    }

    sscanf(buf, "%d\a%d", &tag, &version);
    if ((tag != TAG_VER) || (version != VERSION_1)) {
        printf("Failed tag or version");
        goto end;
    }

    while (gzgets(gz_file, buf, sizeof(buf))) {
        ret = sscanf(buf, "%d", &tag);
        if (tag != TAG_DATA) {
            continue;
        }

        ret = sscanf(buf, "%*[^\a]\a%[^\a]\a%[^\a]\a%[^\n]", str_stu_id, str_name, str_total);
        if (ret != 3) {
            printf("Failed to read student details ret:%d", ret);
            continue;
        }
        printf("Read the data : ID:%s, Name:%s, Total:%s \n", str_stu_id, str_name, str_total);
    }

end:
    gzclose(gz_file);
    return;
}

int main()
{
    save_db();
    read_db();

    return 0;
}
 

Output:

:~/velrajk/sample$ gcc file_list_of_data.c  -lz
:~/velrajk/sample$ ls -l file_gz_db.gz
ls: cannot access file_gz_db.gz: No such file or directory
:~/velrajk/sample$ ./a.out
Read the data : ID:100, Name:Velraj, Total:500
:~/velrajk/sample$ ls -l file_gz_db.gz
-rw-rw-r-- 1 labuser labuser 41 Jul 22 14:44 file_gz_db.gz
:~/velrajk/sample$ gunzip file_gz_db.gz
:~/velrajk/sample$ cat file_gz_db
11
2100Velraj500
:~/velrajk/sample$

Reference:
https://www.lemoda.net/c/gzfile-read/
https://stackoverflow.com/questions/39233004/zlib-gzopen-returns-a-compressed-file-stream-does-it-decompress-the-file
https://github.com/madler/zlib