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;?
}?
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