目录

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;
}


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