C语言函数--E

函数名: ecvt

功 能: 把一个浮点数转换为字符串

用 法: char ecvt(double value, int ndigit, int *decpt, int *sign);

程序例:

#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
int main(void)
{
   char *string;
   double value;
   int dec, sign;
   int ndig = 10;
   clrscr();
   value = 9.876;
   string = ecvt(value, ndig, &dec, &sign);
   printf("string = %s      dec = %d \
   sign = %d\n", string, dec, sign);
   value = -123.45;
   ndig= 15;
   string = ecvt(value,ndig,&dec,&sign);
   printf("string = %s dec = %d sign = %d\n",
   string, dec, sign); 

   value = 0.6789e5; /* scientific
   notation */
   ndig = 5;
   string = ecvt(value,ndig,&dec,&sign);
   printf("string = %s           dec = %d\
   sign = %d\n", string, dec, sign);
   return 0;
} 

函数名: ellipse

功 能: 画一椭圆

用 法: void far ellipse(int x, int y, int stangle, int endangle,

    int xradius, int yradius); 

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 stangle = 0, endangle = 360;
   int xradius = 100, yradius = 50;
   /* initialize graphics, 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 ellipse */
   ellipse(midx, midy, stangle, endangle,
    xradius, yradius);
   /* clean up */
   getch();
   closegraph();
   return 0;
} 

函数名: enable

功 能: 开放硬件中断

用 法: void enable(void);

程序例:

/* ** NOTE:
This is an interrupt service routine. You can NOT compile this program
with Test Stack Overflow turned on and get an executable file which will
operate correctly.
*/
#include <stdio.h>
#include <dos.h>
#include <conio.h>
/* The clock tick interrupt */
#define INTR 0X1C
void interrupt ( *oldhandler)(void);
int count=0;
void interrupt handler(void)
{
/*
   disable interrupts during the handling of the interrupt
*/
   disable();
/* increase the global counter */
   count++;
/*
   re enable interrupts at the end of the handler
*/
   enable();
/* call the old routine */
   oldhandler();
}
int main(void)
{
/* save the old interrupt vector */
   oldhandler = getvect(INTR);
/* install the new interrupt handler */
   setvect(INTR, handler);
/* loop until the counter exceeds 20 */
   while (count < 20)
      printf("count is %d\n",count);
/* reset the old interrupt handler */
   setvect(INTR, oldhandler);
   return 0;
} 

函数名: eof

功 能: 检測文件结束

用 法: int eof(int *handle);

程序例:

#include <sys\stat.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
int main(void)
{
   int handle;
   char msg[] = "This is a test";
   char ch;
   /* create a file */
   handle = open("DUMMY.FIL",
   O_CREAT | O_RDWR,
   S_IREAD | S_IWRITE);
   /* write some data to the file */
   write(handle, msg, strlen(msg));
   /* seek to the beginning of the file */
   lseek(handle, 0L, SEEK_SET);
   /*
      reads chars from the file until hit EOF
   */
   do
   {
      read(handle, &ch, 1);
      printf("%c", ch);
   } while (!eof(handle));
   close(handle);
   return 0;
} 

函数名: exec...

功 能: 装入并执行其他程序的函数

用 法: int execl(char *pathname, char *arg0, arg1, ..., argn, NULL);

 int execle(char *pathname, char *arg0, arg1, ..., argn, NULL,
     char *envp[]);
 int execlp(char *pathname, char *arg0, arg1, .., NULL);
 int execple(char *pathname, char *arg0, arg1, ..., NULL,
      char *envp[]);
 int execv(char *pathname, char *argv[]);
 int execve(char *pathname, char *argv[], char *envp[]);
 int execvp(char *pathname, char *argv[]);
 int execvpe(char *pathname, char *argv[], char *envp[]); 

程序例:

/* execv example */
#include <process.h>
#include <stdio.h>
#include <errno.h>
void main(int argc, char *argv[])
{
   int i;
   printf("Command line arguments:\n");
   for (i=0; i<argc; i++)
      printf("[%2d] : %s\n", i, argv[i]);
   printf("About to exec child with arg1 arg2 ...\n");
   execv("CHILD.EXE", argv);
   perror("exec error");
   exit(1);
} 

函数名: exit

功 能: 终止程序

用 法: void exit(int status);

程序例:

#include <stdlib.h>
#include <conio.h>
#include <stdio.h>
int main(void)
{
   int status;
   printf("Enter either 1 or 2\n");
   status = getch();
   /* Sets DOS errorlevel  */
   exit(status - '0');
/* Note: this line is never reached */
   return 0;
} 

函数名: exp

功 能: 指数函数

用 法: double exp(double x);

程序例:

#include <stdio.h>
#include <math.h>
int main(void)
{
   double result;
   double x = 4.0;
   result = exp(x);
   printf("'e' raised to the power \
   of %lf (e ^ %lf) = %lf\n",
   x, x, result);
   return 0;
} 

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