C语言函数_U起始_C语言教程

C语言函数_U起始_C语言教程

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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