C语言库函数(U类字母)

发布时间:2008年04月03日      浏览次数:935 次
函数名: ultoa
  功 能: 转换一个无符号长整型数为字符串
  用 法: char *ultoa(unsigned long value, char *string, int radix);
  程序例:
  #include <stdlib.h>
  #include <stdio.h>
  int main( void )
  {
   unsigned long lnumber = 3123456789L;
   char string[25];
   ultoa(lnumber,string,10);
   printf("string = %s unsigned long = %lu\n",string,lnumber);
   return 0;
  }
  
  
  
  函数名: ungetc
  功 能: 把一个字符退回到输入流中
  用 法: int ungetc(char c, FILE *stream);
  程序例:
  #include <stdio.h>
  #include <ctype.h>
  int main( void )
  {
   int i=0;
   char ch;
   puts("Input an integer followed by a char:");
   /* read chars until non digit or EOF */
   while((ch = getchar()) != EOF && isdigit(ch))
   i = 10 * i + ch - 48; /* convert ASCII into int value */
   /* if non digit char was read, push it back into input buffer */
   if (ch != EOF)
   ungetc(ch, stdin);
   printf("i = %d, next char in buffer = %c\n", i, getchar());
   return 0;
  }
  
  
  
  函数名: ungetch
  功 能: 把一个字符退回到键盘缓冲区中
  用 法: int ungetch(int c);
  程序例:
  #include <stdio.h>
  #include <ctype.h>
  #include <conio.h>
  int main( void )
  {
   int i=0;
   char ch;
   puts("Input an integer followed by a char:");
   /* read chars until non digit or EOF */
   while((ch = getche()) != EOF && isdigit(ch))
   i = 10 * i + ch - 48; /* convert ASCII into int value */
   /* if non digit char was read, push it back into input buffer */
   if (ch != EOF)
   ungetch(ch);
   printf("\n\ni = %d, next char in buffer = %c\n", i, getch());
   return 0;
  }
  
  
  
  函数名: unixtodos
  功 能: 把日期和时间转换成DOS格式
  用 法: void unixtodos(long utime, struct date *dateptr,
   struct time *timeptr);
  程序例:
  #include <stdio.h>
  #include <dos.h>
  char *month[] = {"---", "Jan", "Feb", "Mar", "Apr", "May", "Jun",
   "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
  #define SECONDS_PER_DAY 86400L /* the number of seconds in one day */
  struct date dt;
  struct time tm;
  int main(void)
  {
   unsigned long val;
  /* get today's date and time */
   getdate(&dt);
   gettime(&tm);
   printf("today is %d %s %d\n", dt.da_day, month[dt.da_mon], dt.da_year);
  /* convert date and time to unix format (number of seconds since Jan 1, 1970 */
   val = dostounix(&dt, &tm);
  /* subtract 42 days worth of seconds */
   val -= (SECONDS_PER_DAY * 42);
  /* convert back to dos time and date */
   unixtodos(val, &dt, &tm);
   printf("42 days ago it was %d %s %d\n",
   dt.da_day, month[dt.da_mon], dt.da_year);
   return 0;
  }
  
  
  
  函数名: unlink
  功 能: 删掉一个文件
  用 法: int unlink(char *filename);
  程序例:
  #include <stdio.h>
  #include <io.h>
  int main(void)
  {
   FILE *fp = fopen("junk.jnk","w");
   int status;
   fprintf(fp,"junk");
   status = access("junk.jnk",0);
   if (status == 0)
   printf("File exists\n");
   else
   printf("File doesn't exist\n");
   fclose(fp);
   unlink("junk.jnk");
   status = access("junk.jnk",0);
   if (status == 0)
   printf("File exists\n");
   else
   printf("File doesn't exist\n");
  
   return 0;
  }
  
  
  
  函数名: unlock
  功 能: 解除文件共享锁
  用 法: int unlock(int handle, long offset, long length);
  程序例:
  #include <io.h>
  #include <fcntl.h>
  #include <sys\stat.h>
  #include <process.h>
  #include <share.h>
  #include <stdio.h>
  int main(void)
  {
   int handle, status;
   long length;
   handle = sopen("c:\\autoexec.bat",O_RDONLY,SH_DENYNO,S_IREAD);
   if (handle < 0)
   {
   printf("sopen failed\n");
   exit(1);
   }
   length = filelength(handle);
   status = lock(handle,0L,length/2);
   if (status == 0)
   printf("lock succeeded\n");
   else
   printf("lock failed\n");
   status = unlock(handle,0L,length/2);
   if (status == 0)
   printf("unlock succeeded\n");
   else
   printf("unlock failed\n");
   close(handle);
   return 0;
  }
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