C函数大全Uu

函数大全(U开头) 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 #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 #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 #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 #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; } 函数名: unlink 功 能: 删掉一个文件 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 #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; }