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; }