C語言函數大全(u開頭)

函數名: ultoa

功能: 轉換一個無符號長整型數為字符串

用法: char *ultoa(unsigned long value, char *string, int radix);

程序例:

#include
#include
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;
}

函數名: ungetc

功能: 把一個字符退回到輸入流中

用法: int ungetc(char c, FILE *stream);

程序例:

#include
#include
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;
}

函數名: ungetch

功能: 把一個字符退回到鍵盤緩沖區中

用法: int ungetch(int c);

程序例:

#include
#include
#include
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;
}

函數名: unixtodos

功能: 把日期和時間轉換成DOS格式

用法: void unixtodos(long utime, struct date *dateptr,

struct time *timeptr);

程序例:

#include
#include
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;
}

函數名: unlink

功能: 刪掉一個文件

用法: int unlink(char *filename);

程序例:

#include
#include
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;
}

函數名: unlock

功能: 解除文件共享鎖

用法: int unlock(int handle, long offset, long length);

程序例:

#include
#include
#include
#include
#include
#include
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;
}