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: 检测文件结束

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: 装入并运行其它程序的函数

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; 
}