E开头的函数

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:

#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;   }