[c函数之e].txt

C常用函数 多了解一些有好处的

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; 
}