c语言库函数(u类字母).txt

较为全面地介绍了C语言的各种库函数

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;  
}