|
C语言库函数大全及应用实例三
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:
＃i nclude
＃i nclude
＃i nclude
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:
＃i nclude
＃i nclude
＃i nclude
＃i nclude
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.
*/
＃i nclude
＃i nclude
＃i nclude
/* 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:
＃i nclude
＃i nclude
＃i nclude
＃i nclude
＃i nclude
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 */
＃i nclude
＃i nclude
＃i nclude
void main(int argc, char *argv[])
{
int i;
printf("Command line arguments:\n");
for (i=0; i
printf("[%2d] : %s\n", i, argv);
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:
＃i nclude
＃i nclude
＃i nclude
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:
＃i nclude
＃i nclude
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;
}
double fabs(double x);
返回双精度x的绝对值。
void far *farcalloc(unsigned long nunits,unsigned long unitsz);
堆中给含有nu从远nits个元素的，每个元素占用unitsz个字节长的数组分配存贮区。
成功是返回指向新分配的内存块的指针；若存贮空间不够，返回NULL。
unsigned long farcoreleft(void);
返回远堆中未用存贮区的大小。
void farfree(void far *block);
释放远堆中以前所分配内存块。
void far *farmalloc(unsigned long nbytes);
从远堆分配长nbytes字节的内存块，返回新地址。
void far *farrealloc(void far *oldblock,unsigned long nbytes);
调整已分配的内存块的大小为nbytes。需要的话，可把块中的内容复制到新位置。要注意：所有的可用的RAM可被分配，大于64K的块可被分配。
远指针用于存取被分配的块。返回重新分配的内存块的地址。若存贮块重新分配失败，返回NULL。
struct fcb {
char fcb_drive; /* 0 = default, 1 = A, 2 = B */
char fcb_name[8]; /* File name */
char fcb_ext[3]; /* File extension */
short fcb_curblk; /* Current block number */
short fcb_recsize; /* Logical record size in bytes */
long fcb_filsize; /* File size in bytes */
short fcb_date; /* Date file was last written */
char fcb_resv[10]; /* Reserved for DOS */
char fcb_currec; /* Current record in block */
long fcb_random; /* Random record number */
}; | 
