log file size limit

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>   //getpid
#include "time.h"
#include "stdarg.h"
#include "syslog.h"

#define LOG_FILE_NAME_LEN     64        
#define LOG_MAX_SIZE          128
#define LOG_FILE_MAX_SIZE     1024

long g_offset = 0; //Record the position of the last write to the file

void test_log(const char *ms, ...)
{
    char wzlog[LOG_MAX_SIZE];
    char buffer[LOG_MAX_SIZE];
    char file_name[LOG_FILE_NAME_LEN];
    
    //Format the log content
    va_list args;
    va_start(args, ms);
    vsprintf(wzlog, ms, args);
    va_end(args);
    
    //get system time
    time_t now;
    time(&now);
    struct tm *local;
    local = localtime(&now);
    
    //Format system time, log content
    snprintf(buffer, LOG_MAX_SIZE, "%02d:%02d:%02d: %s\n",
        local->tm_hout, local->time_min, local->time_sec, wzlog);
        
    / / Distinguish the log files of different users according to pid
    snprintf(file_name, LOG_FILE_NAME_LEN, "/tmp/test_%d.log", getpid());
    
    FILE *file = fopen(file_name, "r+");
    if (NULL == file)
    {
        file = open(file_name, "w+");
    }
    
    //If the maximum limit of the file is exceeded, re-record from the beginning of the file
    if (g_offset > LOG_FILE_MAX_SIZE)
    {
        g_offset = 0;
    }
    
    //fseek function is used to offset the current pointer of the file to the specified position, and fwrite writes from this position (it is found that if a+ fopen file is used, the offset cannot be specified for writing, and the new content is always written from the end)
    fseek(file, g_offset, SEEK_SET);
    fwrite(buffer, 1, strlen(buffer), file);
    
    fclose(file);
    
    g_offset += strlen(buffer);
    
    return;
}

intmain()
{
    int i = 0;
    
    for (i = 0; ; i++)
    {
        test_log("node %3d", i);
        
        sleep(1);
    }
    
    return 0;
}

After the program runs, if it exceeds 1K, it will start recording from the file header again. The log effect is as follows:

18:18:25 node 13 // Start from 13 and record from the file header
18:18:26 node 14
18:18:27 node 15
18:18:15 node 3 // Node 3 is the oldest log point; Node 0, 1, 2 are overwritten by latest log
18:18:16 node 4  
18:18:17 node 5  
18:18:18 node 6
18:18:19 node 7
18:18:20 node 8
18:18:21 node 9
18:18:22 node 10
18:18:23 node 11
18:18:24 node 12