C语言库函数 (C类字母)

  [ 发表日期:2002-1-4 9:28:46 ]
  函数名: cabs
  功 能: 计算复数的绝对值
  用 法: double cabs(strUCt complex z);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  struct complex z;
  double val;
  z.x = 2.0;
  z.y = 1.0;
  val = cabs(z);
  printf("The absolute value of %.2lfi %.2lfj is %.2lf", z.x, z.y, val);
  return 0;
  }
  函数名: calloc
  功 能: 分配主存储器
  用 法: void *calloc(size_t nelem, size_t elsize);
  程序例:
  #include <stdio.h>
  #include <alloc.h>
  int main(void)
  {
  char *str = NULL;
  /* allocate memory for string */
  str = calloc(10, sizeof(char));
  /* copy "Hello" into string */
  strcpy(str, "Hello");
  /* display string */
  printf("String is %s\n", str);
  /* free memory */
  free(str);
  return 0;
  }
  函数名: ceil
  功 能: 向上舍入
  用 法: double ceil(double x);
  程序例:
  #include <math.h>
  #include <stdio.h>
  int main(void)
  {
  double number = 123.54;
  double down, up;
  down = floor(number);
  up = ceil(number);
  printf("original number %5.2lf\n", number);
  printf("number rounded down %5.2lf\n", down);
  printf("number rounded up %5.2lf\n", up);
  return 0;
  }
  函数名: cgets
  功 能: 从控制台读字符串
  用 法: char *cgets(char *str);
  程序例:
  #include <stdio.h>
  #include <conio.h>
  int main(void)
  {
  char buffer[83];
  char *p;
  /* There's space for 80 characters plus the NULL terminator */
  buffer[0] = 81;
  printf("Input some chars:");
  p = cgets(buffer);
  printf("\ncgets read %d characters: \"%s\"\n", buffer[1], p);
  printf("The returned pointer is %p, buffer[0] is at %p\n", p, &buffer);
  /* Leave room for 5 characters plus the NULL terminator */
  buffer[0] = 6;
  printf("Input some chars:");
  p = cgets(buffer);
  printf("\ncgets read %d characters: \"%s\"\n", buffer[1], p);
  printf("The returned pointer is %p, buffer[0] is at %p\n", p, &buffer);
  return 0;
  }
  函数名: chdir
  功 能: 改变工作目录
  用 法: int chdir(const char *path);
  程序例:
  #include <stdio.h>
  #include <stdlib.h>
  #include <dir.h>
  char old_dir[MAXDIR];
  char new_dir[MAXDIR];
  int main(void)
  {
  if (getcurdir(0, old_dir))
  {
  perror("getcurdir()");
  exit(1);
  }
  printf("Current Directory is: \\%s\n", old_dir);
  if (chdir("\\"))
  {
  perror("chdir()");
  exit(1);
  }
  if (getcurdir(0, new_dir))
  
   {
  perror("getcurdir()");
  exit(1);
  }
  printf("Current directory is now: \\%s\n", new_dir);
  printf("\nChanging back to orignal directory: \\%s\n", old_dir);
  if (chdir(old_dir))
  {
  perror("chdir()");
  exit(1);
  }
  return 0;
  }
  函数名: _chmod, chmod
  功 能: 改变文件的访问方式
  用 法: int chmod(const char *filename, int permiss);
  程序例:
  #include <sys\stat.h>
  #include <stdio.h>
  #include <io.h>
  void make_read_only(char *filename);
  int main(void)
  {
  make_read_only("NOTEXIST.FIL");
  make_read_only("MYFILE.FIL");
  return 0;
  }
  void make_read_only(char *filename)
  {
  int stat;
  stat = chmod(filename, S_IREAD);
  if (stat)
  printf("Couldn't make %s read-only\n", filename);
  else
  printf("Made %s read-only\n", filename);
  }
  函数名: chsize
  功 能: 改变文件大小
  用 法: int chsize(int handle, long size);
  程序例:
  #include <string.h>
  #include <fcntl.h>
  #include <io.h>
  int main(void)
  {
  int handle;
  char buf[11] = "0123456789";
  /* create text file containing 10 bytes */
  handle = open("DUMMY.FIL", O_CREAT);
  write(handle, buf, strlen(buf));
  /* truncate the file to 5 bytes in size */
  chsize(handle, 5);
  /* close the file */
  close(handle);
  return 0;
  }
  函数名: circle
  功 能: 在给定半径以(x, y)为圆心画圆
  用 法: void far circle(int x, int y, int radius);
  程序例:
  #include <graphics.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <conio.h>
  int main(void)
  {
  /* request auto detection */
  int gdriver = DETECT, gmode, errorcode;
  int midx, midy;
  int radius = 100;
  /* initialize graphics and local variables */
  initgraph(&gdriver, &gmode, "");
  /* read result of initialization */
  errorcode = graphresult();
  if (errorcode != grOk) /* an error occurred */
  {
  printf("Graphics error: %s\n", grapherrormsg(errorcode));
  printf("Press any key to halt:");
  getch();
  exit(1); /* terminate with an error code */
  }
  midx = getmaxx() / 2;
  midy = getmaxy() / 2;
  setcolor(getmaxcolor());
  /* draw the circle */
  circle(midx, midy, radius);
  /* clean up */
  getch();
  closegraph();
  return 0;
  }
  函数名: cleardevice
  功 能: 清除图形屏幕
  用 法: void far cleardevice(void);
  程序例:
  #include <graphics.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <conio.h>
  int main(void)
  {
  /* request auto detection */
  int gdriver = DETECT, gmode, errorcode;
  int midx, midy;
  /* initialize graphics and local variables */
  initgraph(&gdriver, &gmode, "");
  /* read result of initialization */
  errorcode = graphresult();
  if (errorcode != grOk) /* an error occurred */
  
   {
  printf("Graphics error: %s\n", grapherrormsg(errorcode));
  printf("Press any key to halt:");
  getch();
  exit(1); /* terminate with an error code */
  }
  midx = getmaxx() / 2;
  midy = getmaxy() / 2;
  setcolor(getmaxcolor());
  /* for centering screen messages */
  settextjustify(CENTER_TEXT, CENTER_TEXT);
  /* output a message to the screen */
  outtextxy(midx, midy, "press any key to clear the screen:");
  /* wait for a key */
  getch();
  /* clear the screen */
  cleardevice();
  /* output another message */
  outtextxy(midx, midy, "press any key to quit:");
  /* clean up */
  getch();
  closegraph();
  return 0;
  }
  函数名: clearerr
  功 能: 复位错误标志
  用 法:void clearerr(FILE *stream);
  程序例:
  #include <stdio.h>
  int main(void)
  {
  FILE *fp;
  char ch;
  /* open a file for writing */
  fp = fopen("DUMMY.FIL", "w");
  /* force an error condition by attempting to read */
  ch = fgetc(fp);
  printf("%c\n",ch);
  if (ferror(fp))
  {
  /* display an error message */
  printf("Error reading from DUMMY.FIL\n");
  /* reset the error and EOF indicators */
  clearerr(fp);
  }
  fclose(fp);
  return 0;
  }
  函数名: clearviewport
  功 能: 清除图形视区
  用 法: void far clearviewport(void);
  程序例:
  #include <graphics.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <conio.h>
  #define CLIP_ON 1 /* activates clipping in viewport */
  int main(void)
  {
  /* request auto detection */
  int gdriver = DETECT, gmode, errorcode;
  int ht;
  /* initialize graphics and local variables */
  initgraph(&gdriver, &gmode, "");
  /* read result of initialization */
  errorcode = graphresult();
  if (errorcode != grOk) /* an error occurred */
  {
  printf("Graphics error: %s\n", grapherrormsg(errorcode));
  printf("Press any key to halt:");
  getch();
  exit(1); /* terminate with an error code */
  }
  setcolor(getmaxcolor());
  ht = textheight("W");
  /* message in default full-screen viewport */
  outtextxy(0, 0, "* <-- (0, 0) in default viewport");
  /* create a smaller viewport */
  setviewport(50, 50, getmaxx()-50, getmaxy()-50, CLIP_ON);
  /* display some messages */
  outtextxy(0, 0, "* <-- (0, 0) in smaller viewport");
  outtextxy(0, 2*ht, "Press any key to clear viewport:");
  /* wait for a key */
  getch();
  /* clear the viewport */
  clearviewport();
  /* output another message */
  outtextxy(0, 0, "Press any key to quit:");
  /* clean up */
  getch();
  closegraph();
  return 0;
  }
  函数名: _close, close
  功 能: 关闭文件句柄
  用 法: int close(int handle);
  程序例:
  #include <string.h>
  #include <stdio.h>
  #include <fcntl.h>
  
   #include <io.h>
  main()
  {
  int handle;
  char buf[11] = "0123456789";
  /* create a file containing 10 bytes */
  handle = open("NEW.FIL", O_CREAT);
  if (handle > -1)
  {
  write(handle, buf, strlen(buf));
  /* close the file */
  close(handle);
  }
  else
  {
  printf("Error opening file\n");
  }
  return 0;
  }
  函数名: clock
  功 能: 确定处理器时间
  用 法: clock_t clock(void);
  程序例:
  #include <time.h>
  #include <stdio.h>
  #include <dos.h>
  int main(void)
  {
  clock_t start, end;
  start = clock();
  delay(2000);
  end = clock();
  printf("The time was: %f\n", (end - start) / CLK_TCK);
  return 0;
  }
  函数名: closegraph
  功 能: 关闭图形系统
  用 法: void far closegraph(void);
  程序例:
  #include <graphics.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <conio.h>
  int main(void)
  {
  /* request auto detection */
  int gdriver = DETECT, gmode, errorcode;
  int x, y;
  /* initialize graphics mode */
  initgraph(&gdriver, &gmode, "");
  /* read result of initialization */
  errorcode = graphresult();
  if (errorcode != grOk) /* an error
  occurred */
  {
  printf("Graphics error: %s\n", grapherrormsg(errorcode));
  printf("Press any key to halt:");
  getch();
  exit(1); /* terminate with an error code */
  }
  x = getmaxx() / 2;
  y = getmaxy() / 2;
  /* output a message */
  settextjustify(CENTER_TEXT, CENTER_TEXT);
  outtextxy(x, y, "Press a key to close the graphics system:");
  /* wait for a key */
  getch();
  /* closes down the graphics system */
  closegraph();
  printf("We're now back in text mode.\n");
  printf("Press any key to halt:");
  getch();
  return 0;
  }
  函数名: clreol
  功 能: 在文本窗口中清除字符到行末
  用 法: void clreol(void);
  程序例:
  #include <conio.h>
  int main(void)
  {
  clrscr();
  cprintf("The function CLREOL clears all characters from the\r\n");
  cprintf("cursor position to the end of the line within the\r\n");
  cprintf("current text window, without moving the cursor.\r\n");
  cprintf("Press any key to continue . . .");
  gotoxy(14, 4);
  getch();
  clreol();
  getch();
  return 0;
  }
  函数名: clrscr
  功 能: 清除文本模式窗口
  用 法: void clrscr(void);
  程序例:
  #include <conio.h>
  int main(void)
  {
  int i;
  clrscr();
  for (i = 0; i < 20; i++)
  cprintf("%d\r\n", i);
  cprintf("\r\nPress any key to clear screen");
  getch();
  clrscr();
  cprintf("The screen has been cleared!");
  getch();
  return 0;
  }
  函数名: coreleft
  功 能: 返回未使用内存的大小
  用 法: unsigned coreleft(void);
  程序例:
  #include <stdio.h>
  #include <alloc.h>
  int main(void)
  
   {
  printf("The difference between the highest allocated block and\n");
  printf("the top of the heap is: %lu bytes\n", (unsigned long) coreleft());
  return 0;
  }
  函数名: cos
  功 能: 余弦函数
  用 法: double cos(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = cos(x);
  printf("The cosine of %lf is %lf\n", x, result);
  return 0;
  }
  函数名: cosh
  功 能: 双曲余弦函数
  用 法: dluble cosh(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = cosh(x);
  printf("The hyperboic cosine of %lf is %lf\n", x, result);
  return 0;
  }
  函数名: country
  功 能: 返回与国家有关的信息
  用 法: struct COUNTRY *country(int countrycode, struct country *country);
  程序例:
  #include <dos.h>
  #include <stdio.h>
  #define USA 0
  int main(void)
  {
  struct COUNTRY country_info;
  country(USA, &country_info);
  printf("The currency symbol for the USA is: %s\n",
  country_info.co_curr);
  return 0;
  }
  函数名: cprintf
  功 能: 送格式化输出至屏幕
  用 法: int cprintf(const char *format[, argument, ...]);
  程序例:
  #include <conio.h>
  int main(void)
  {
  /* clear the screen */
  clrscr();
  /* create a text window */
  window(10, 10, 80, 25);
  /* output some text in the window */
  cprintf("Hello world\r\n");
  /* wait for a key */
  getch();
  return 0;
  }
  函数名: cputs
  功 能: 写字符到屏幕
  用 法: void cputs(const char *string);
  程序例:
  #include <conio.h>
  int main(void)
  {
  /* clear the screen */
  clrscr();
  /* create a text window */
  window(10, 10, 80, 25);
  /* output some text in the window */
  cputs("This is within the window\r\n");
  /* wait for a key */
  getch();
  return 0;
  }
  函数名: _creat creat
  功 能: 创建一个新文件或重写一个已存在的文件
  用 法: int creat (const char *filename, int permiss);
  程序例:
  #include <sys\stat.h>
  #include <string.h>
  #include <fcntl.h>
  #include <io.h>
  int main(void)
  {
  int handle;
  char buf[11] = "0123456789";
  /* change the default file mode from text to binary */
  _fmode = O_BINARY;
  /* create a binary file for reading and writing */
  handle = creat("DUMMY.FIL", S_IREAD S_IWRITE);
  /* write 10 bytes to the file */
  write(handle, buf, strlen(buf));
  /* close the file */
  close(handle);
  return 0;
  }
  函数名: creatnew
  功 能: 创建一个新文件
  用 法: int creatnew(const char *filename, int attrib);
  程序例:
  #include <string.h>
  #include <stdio.h>
  #include <errno.h>
  #include <dos.h>
  
   #include <io.h>
  int main(void)
  {
  int handle;
  char buf[11] = "0123456789";
  /* attempt to create a file that doesn't already exist */
  handle = creatnew("DUMMY.FIL", 0);
  if (handle == -1)
  printf("DUMMY.FIL already exists.\n");
  else
  {
  printf("DUMMY.FIL successfully created.\n");
  write(handle, buf, strlen(buf));
  close(handle);
  }
  return 0;
  }
  函数名: creattemp
  功 能: 创建一个新文件或重写一个已存在的文件
  用 法: int creattemp(const char *filename, int attrib);
  程序例:
  #include <string.h>
  #include <stdio.h>
  #include <io.h>
  int main(void)
  {
  int handle;
  char pathname[128];
  strcpy(pathname, "\\");
  /* create a unique file in the root directory */
  handle = creattemp(pathname, 0);
  printf("%s was the unique file created.\n", pathname);
  close(handle);
  return 0;
  }
  函数名: cscanf
  功 能: 从控制台执行格式化输入
  用 法: int cscanf(char *format[,argument, ...]);
  程序例:
  #include <conio.h>
  int main(void)
  {
  char string[80];
  /* clear the screen */
  clrscr();
  /* Prompt the user for input */
  cprintf("Enter a string with no spaces:");
  /* read the input */
  cscanf("%s", string);
  /* display what was read */
  cprintf("\r\nThe string entered is: %s", string);
  return 0;
  }
  函数名: ctime
  功 能: 把日期和时间转换为字符串
  用 法: char *ctime(const time_t *time);
  程序例:
  #include <stdio.h>
  #include <time.h>
  int main(void)
  {
  time_t t;
  time(&t);
  printf("Today's date and time: %s\n", ctime(&t));
  return 0;
  }
  函数名: ctrlbrk
  功 能: 设置Ctrl-Break处理程序
  用 法: void ctrlbrk(*fptr)(void);
  程序例:
  #include <stdio.h>
  #include <dos.h>
  #define ABORT 0
  int c_break(void)
  {
  printf("Control-Break pressed. Program aborting ...\n");
  return (ABORT);
  }
  int main(void)
  {
  ctrlbrk(c_break);
  for(;;)
  {
  printf("Looping... Press <Ctrl-Break> to quit:\n");
  }
  return 0;
  }