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\", string, dec, sign);

value = -123.45;

ndig= 15;

string = ecvt(value,ndig,&dec,&sign);

printf("string = %s dec = %d sign = %d\",

string, dec, sign);

value = 0.6789e5; /* scientific

notation */

ndig = 5;

string = ecvt(value,ndig,&dec,&sign);

printf("string = %s dec = %d\\

sign = %d\", 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\",

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\",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:\");

for (i=0; i<argc; i++)

printf("[%2d] : %s\", i, argv[i]);

printf("About to exec child with arg1 arg2 ...\");

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\");

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\",

x, x, result);

return 0;

}