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(qū)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;
    }