#include <stdio.h> 
#include <time.h> 
#include <sys/time.h> 
 
char *mon_full[12] = { 
  "January", "February", "March", "April", 
  "May", "June", "July", "August", 
  "September", "October", "November", "December" 
}; 
 
char *mon_short[12] = { 
  "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" 
}; 
 
char *day_full[7] = { 
  "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" 
}; 
 
char *day_short[7]={ 
  "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" 
}; 
 
#define isleap(year) ((((year) % 4) == 0 && ((year) % 100) != 0) || ((year) % 400)==0) 
#define YEAR_BASE 1900 
 
static int day_tab[2][12] = { 
  {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, 
  {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31} 
}; 
 
int date(char *,long int ,char **); 
 
int date(char *format,long int timestamp,char **ret){ 
 
  char buf[11]={0}; 
  char *ret_tmp; 
  char chr; 
  int cnt=0; 
  int mem_size=0,str_len=0; 
  int num_tmp=0,wd,yd,fd,wk; 
  struct tm *tm_date; 
  time_t time_date; 
 
  if(timestamp<0){ 
    time_date=time(NULL); 
  }else{ 
    time_date=timestamp; 
  } 
     
  while((chr=*(format+cnt))){ 
 
    switch(chr){ 
 
      case '\\': 
        ++cnt; 
        ++mem_size; 
        break; 
      case 'U': 
        mem_size+=10; 
        break; 
      case 'Y': 
        mem_size+=4; 
        break; 
      case 'B': 
      case 'D': 
      case 'M': 
        mem_size+=3; 
        break; 
      case 'l': 
      case 'F': 
        mem_size+=9;//l Wednesday,F September 
        break; 
      case 'g': 
      case 'G': 
      case 'h': 
      case 'm': 
      case 'd': 
      case 'H': 
      case 'i': 
      case 'j': 
      case 's': 
      case 'A': 
      case 'a': 
      case 'n': 
      case 't': 
      case 'W': 
      case 'y': 
      case 'z': 
        mem_size+=2; 
        break; 
      case 'I': 
      case 'L': 
      case 'w': 
      default: 
        ++mem_size; 
        break; 
 
    } 
 
    ++cnt; 
 
  } 
 
  (*ret)=(char *)malloc(sizeof(char)*mem_size+1); 
  memset((*ret),0x0,sizeof(char)*mem_size+1); 
  ret_tmp=(*ret); 
   
  cnt=0; 
  tm_date=gmtime((time_t *)&time_date); 
 
  while((chr=*(format+cnt))){ 
 
    switch(chr){ 
 
      case '\\': 
        ++cnt; 
        *(*ret)=*(format+cnt); 
        ++(*ret); 
        break; 
      case 'U': 
        sprintf(buf,"%ld",time_date); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 'Y': 
        sprintf(buf,"%04d",(tm_date->tm_year)+YEAR_BASE); 
        memcpy((*ret),buf,4); 
        (*ret)+=4; 
        break; 
      case 'B': 
        num_tmp=(((((long)time_date)-(((long)time_date)- 
        ((((long)time_date)%86400)+3600)))*10)/864); 
        while(num_tmp<0){ 
          num_tmp+=1000; 
        } 
        num_tmp=num_tmp%1000; 
        sprintf(buf,"%03d",num_tmp); 
        memcpy((*ret),buf,3); 
        (*ret)+=3; 
        break; 
      case 'D': 
        memcpy((*ret),day_short[tm_date->tm_wday],3); 
        (*ret)+=3; 
        break; 
      case 'M': 
        memcpy((*ret),mon_short[tm_date->tm_mon],3); 
        (*ret)+=3; 
        break; 
      case 'l': 
        str_len=strlen(day_full[tm_date->tm_wday]); 
        memcpy((*ret),day_full[tm_date->tm_wday],str_len); 
        (*ret)+=str_len; 
        break; 
      case 'F': 
        str_len=strlen(mon_full[tm_date->tm_mon]); 
        memcpy((*ret),mon_full[tm_date->tm_mon],str_len); 
        (*ret)+=str_len; 
        break; 
      case 'g': 
        num_tmp=tm_date->tm_hour%12; 
        if(num_tmp==0) num_tmp=12; 
        sprintf(buf,"%d",num_tmp); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 'G': 
        sprintf(buf,"%d",tm_date->tm_hour); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 'h': 
        num_tmp=tm_date->tm_hour%12; 
        if(num_tmp==0) num_tmp=12; 
        sprintf(buf,"%02d",num_tmp); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=2; 
        break; 
      case 'm': 
        sprintf(buf,"%02d",(tm_date->tm_mon)+1); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'd': 
        sprintf(buf,"%02d",tm_date->tm_mday); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'H': 
        sprintf(buf,"%02d",tm_date->tm_hour); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'i': 
        sprintf(buf,"%02d",tm_date->tm_min); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'j': 
        sprintf(buf,"%d",tm_date->tm_mday); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 's': 
        sprintf(buf,"%02d",tm_date->tm_sec); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'A': 
        memcpy((*ret),(tm_date->tm_hour>=12 ? "PM" : "AM"),2); 
        (*ret)+=2; 
        break; 
      case 'a': 
        memcpy((*ret),(tm_date->tm_hour>=12 ? "pm" : "am"),2); 
        (*ret)+=2; 
        break; 
      case 'n': 
        sprintf(buf,"%d",(tm_date->tm_mon)+1); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 't': 
        sprintf(buf,"%d",day_tab[isleap((tm_date->tm_year+YEAR_BASE))][tm_date->tm_mon]); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'W': 
        wd=(tm_date->tm_wday==0 ? 6 : tm_date->tm_wday-1); /* weekday */ 
        yd=tm_date->tm_yday+1;  /* days since January 1st */ 
 
        fd=(7+wd-yd%7+1)%7; /* weekday (1st January) */ 
 
        /* week is a last year week (52 or 53) */ 
        if((yd<=7-fd)&&fd>3){ 
          wk=((fd==4||(fd==5&&isleap((tm_date->tm_year+YEAR_BASE-1)))) ? 53 : 52); 
        } 
        /* week is a next year week (1) */ 
        else if(isleap((tm_date->tm_year+YEAR_BASE))+365-yd<3-wd){ 
          wk=1; 
        } 
        /* normal week */ 
        else{ 
          wk=(yd+6-wd+fd)/7-(fd>3); 
        } 
 
        sprintf(buf,"%d",wk);  /* SAFE */ 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 'y': 
        sprintf(buf,"%02d",((tm_date->tm_year)%100)); 
        memcpy((*ret),buf,2); 
        (*ret)+=2; 
        break; 
      case 'z': 
        sprintf(buf,"%d",tm_date->tm_yday); 
        str_len=strlen(buf); 
        memcpy((*ret),buf,str_len); 
        (*ret)+=str_len; 
        break; 
      case 'I': 
        sprintf(buf,"%d",tm_date->tm_isdst); 
        memcpy((*ret),buf,1); 
        ++(*ret); 
        break; 
      case 'L': 
        sprintf(buf,"%d",(isleap((tm_date->tm_year+YEAR_BASE)) ? 1 : 0)); 
        memcpy((*ret),buf,1); 
        ++(*ret); 
        break; 
      case 'w': 
        sprintf(buf,"%d",tm_date->tm_wday); 
        memcpy((*ret),buf,1); 
        ++(*ret); 
        break; 
      default: 
        *(*ret)=chr; 
        ++(*ret); 
        break; 
 
    } 
 
    ++cnt; 
 
  } 
 
  (*ret)=ret_tmp; 
 
  return 0; 
 
} 
 
EXAMPLE CODE BELOW 
 
#include <stdio.h> 
#include <date.h> 
 
int main(int argc,char **argv){ 
 
  char *format="\\suppor\\te\\d \\l\\e\\t\\t\\er\\s : \\Y\\m\\d\\H\\i\\s\\A\\a\\B\\D\\l\\F\\g\\G\\h\\I\\j\\L\\M\\n\\t\\w\\W\\U\\y\\Z \n\\ex\\a\\mp\\l\\e\\s : Y년 m월 d일 (A/a) H시 i분 s초 D l B F g G h I j L M n t w W U y z"; 
  char *ret=NULL; 
   
  date(format,-1,&ret);  
 
  printf("%s\n",ret); 
 
  free(ret); 
 
  return 0; 
 
}