C语言库函数 （E类字母）

核心提示：[ 发表日期：2002-1-4 9:28:46 ]

[ 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 <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: /* ** 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\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;
}