C语言库函数 （E类字母）

[ 发表日期：2002-1-4 9:28:46

]

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

#include

#include

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

#include

#include

#include

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

#include

#include

/* 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

#include

#include

#include

#include

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

#include

#include

void main(int argc, char

*argv[])

{

int i;

printf("Command line

arguments:

");

for (i=0; 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

#include

#include

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

#include

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;

}