wdg_022c.txt

c编程宝典,详细介绍有关c的资料

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 */