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C语言库函数(E类字母)

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 <sysstat.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;
}

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