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<title>网上学堂 --> C语言编程宝典之一 -->函数名: u</title>
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<td bgcolor="#FFE6B0" bordercolor="#8080FF" class="p9"><font
color="#BB0000">导航条：--></font> <a
href="../../index.html">网上学堂</a> --> <a
href="../tcindex.htm"><font face="宋体">C</font>语言编程宝典之一</a>
-->函数名: u</td>
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<td bordercolor="#8080FF" class="p9"><p>函数名: ultoa <br>
功 能:
转换一个无符号长整型数为字符串 <br>
用 法: char *ultoa(unsigned long value, char
*string, int radix); <br>
程序例: </p>
<p>#include <stdlib.h> <br>
#include <stdio.h> </p>
<p>int main( void ) <br>
{ <br>
unsigned long lnumber = 3123456789L; <br>
char string[25]; </p>
<p> ultoa(lnumber,string,10); <br>
printf("string = %s unsigned long
= %lu\n",string,lnumber); </p>
<p> return 0; <br>
} <br>
<br>
<br>
</p>
<p>函数名: ungetc <br>
功 能: 把一个字符退回到输入流中 <br>
用 法: int ungetc(char c, FILE *stream); <br>
程序例: </p>
<p>#include <stdio.h> <br>
#include <ctype.h> </p>
<p>int main( void ) <br>
{ <br>
int i=0; <br>
char ch; </p>
<p> puts("Input an integer followed by a
char:"); </p>
<p> /* read chars until non digit or EOF */ <br>
while((ch = getchar()) != EOF &&
isdigit(ch)) <br>
i = 10 * i + ch - 48; /*
convert ASCII into int value */ </p>
<p> /* if non digit char was read, push it
back into input buffer */ <br>
if (ch != EOF) <br>
ungetc(ch, stdin); </p>
<p> printf("i = %d, next char in buffer
= %c\n", i, getchar()); <br>
return 0; <br>
} <br>
<br>
<br>
</p>
<p>函数名: ungetch <br>
功 能: 把一个字符退回到键盘缓冲区中
<br>
用 法: int ungetch(int c); <br>
程序例: </p>
<p>#include <stdio.h> <br>
#include <ctype.h> <br>
#include <conio.h> </p>
<p>int main( void ) <br>
{ <br>
int i=0; <br>
char ch; </p>
<p> puts("Input an integer followed by a
char:"); </p>
<p> /* read chars until non digit or EOF */ <br>
while((ch = getche()) != EOF &&
isdigit(ch)) <br>
i = 10 * i + ch - 48; /*
convert ASCII into int value */ </p>
<p> /* if non digit char was read, push it
back into input buffer */ <br>
if (ch != EOF) <br>
ungetch(ch); </p>
<p> printf("\n\ni = %d, next char in
buffer = %c\n", i, getch()); <br>
return 0; <br>
} <br>
<br>
<br>
</p>
<p>函数名: unixtodos <br>
功 能: 把日期和时间转换成DOS格式 <br>
用 法: void unixtodos(long utime, struct date
*dateptr, <br>
struct time *timeptr); <br>
程序例: </p>
<p>#include <stdio.h> <br>
#include <dos.h> </p>
<p>char *month[] = {"---", "Jan",
"Feb", "Mar", "Apr",
"May", "Jun", <br>
"Jul", "Aug", "Sep",
"Oct", "Nov", "Dec"}; </p>
<p>#define SECONDS_PER_DAY 86400L /* the number of
seconds in one day */ </p>
<p>struct date dt; <br>
struct time tm; </p>
<p>int main(void) <br>
{ <br>
unsigned long val; </p>
<p>/* get today's date and time */ <br>
getdate(&dt); <br>
gettime(&tm); <br>
printf("today is %d %s %d\n",
dt.da_day, month[dt.da_mon], dt.da_year); </p>
<p>/* convert date and time to unix format (number of
seconds since Jan 1, 1970 */ <br>
val = dostounix(&dt, &tm); <br>
/* subtract 42 days worth of seconds */ <br>
val -= (SECONDS_PER_DAY * 42); </p>
<p>/* convert back to dos time and date */ <br>
unixtodos(val, &dt, &tm); <br>
printf("42 days ago it was %d %s
%d\n", <br>
dt.da_day,
month[dt.da_mon], dt.da_year); <br>
return 0; <br>
} <br>
<br>
<br>
</p>
<p>函数名: unlink <br>
功 能: 删掉一个文件 <br>
用 法: int unlink(char *filename); <br>
程序例: </p>
<p>#include <stdio.h> <br>
#include <io.h> </p>
<p>int main(void) <br>
{ <br>
FILE *fp =
fopen("junk.jnk","w"); <br>
int status; </p>
<p> fprintf(fp,"junk"); </p>
<p> status = access("junk.jnk",0); <br>
if (status == 0) <br>
printf("File
exists\n"); <br>
else <br>
printf("File doesn't
exist\n"); </p>
<p> fclose(fp); <br>
unlink("junk.jnk"); <br>
status = access("junk.jnk",0); <br>
if (status == 0) <br>
printf("File
exists\n"); <br>
else <br>
printf("File doesn't
exist\n"); <br>
</p>
<p> return 0; <br>
} <br>
<br>
<br>
</p>
<p>函数名: unlock <br>
功 能: 解除文件共享锁 <br>
用 法: int unlock(int handle, long offset, long
length); <br>
程序例: </p>
<p>#include <io.h> <br>
#include <fcntl.h> <br>
#include <sys\stat.h> <br>
#include <process.h> <br>
#include <share.h> <br>
#include <stdio.h> </p>
<p>int main(void) <br>
{ <br>
int handle, status; <br>
long length; </p>
<p> handle =
sopen("c:\\autoexec.bat",O_RDONLY,SH_DENYNO,S_IREAD);
</p>
<p> if (handle < 0) <br>
{ <br>
printf("sopen
failed\n"); <br>
exit(1); <br>
} </p>
<p> length = filelength(handle); <br>
status = lock(handle,0L,length/2); </p>
<p> if (status == 0) <br>
printf("lock
succeeded\n"); <br>
else <br>
printf("lock
failed\n"); </p>
<p> status = unlock(handle,0L,length/2); </p>
<p> if (status == 0) <br>
printf("unlock
succeeded\n"); <br>
else <br>
printf("unlock
failed\n"); </p>
<p> close(handle); <br>
return 0; <br>
} </p>
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