C语言库函数大全及应用实例八

原文:C语言库函数大全及应用实例八

                                           [编程资料]C语言库函数大全及应用实例八

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函数名: kbhit
功 能: 检查当前按下的键
用 法: int kbhit(void);
程序例:

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int main(void)
{
cprintf("Press any key to continue:");
while (!kbhit()) /* do nothing */ ;
cprintf("\r\nA key was pressed...\r\n");
return 0;
}

函数名: keep
功 能: 退出并继续驻留
用 法: void keep(int status, int size);
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. Due to the nature of this
function the formula used to compute
the number of paragraphs may not
necessarily work in all cases. Use with
care! Terminate Stay Resident (TSR)
programs are complex and no other support
for them is provided. Refer to the
MS-DOS technical documentation
for more information. */
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/* The clock tick interrupt */
#define INTR 0x1C
/* Screen attribute (blue on grey) */
#define ATTR 0x7900

/* reduce heaplength and stacklength
to make a smaller program in memory */
extern unsigned _heaplen = 1024;
extern unsigned _stklen = 512;

void interrupt ( *oldhandler)(void);

void interrupt handler(void)
{
unsigned int (far *screen)[80];
static int count;

/* For a color screen the video memory
is at B800:0000. For a monochrome
system use B000:000 */
screen = MK_FP(0xB800,0);

/* increase the counter and keep it
within 0 to 9 */
count++;
count %= 10;

/* put the number on the screen */
screen[0][79] = count + '0' + ATTR;

/* call the old interrupt handler */
oldhandler();
}

int main(void)
{

/* get the address of the current clock
tick interrupt */
oldhandler = getvect(INTR);

/* install the new interrupt handler */
setvect(INTR, handler);

/* _psp is the starting address of the
program in memory. The top of the stack
is the end of the program. Using _SS and
_SP together we can get the end of the
stack. You may want to allow a bit of
saftey space to insure that enough room
is being allocated ie:
(_SS + ((_SP + safety space)/16) - _psp)
*/
keep(0, (_SS + (_SP/16) - _psp));
return 0;
}

函数名: kbhit
功 能: 检查当前按下的键
用 法: int kbhit(void);
程序例:

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int main(void)
{
cprintf("Press any key to continue:");
while (!kbhit()) /* do nothing */ ;
cprintf("\r\nA key was pressed...\r\n");
return 0;
}

函数名: keep
功 能: 退出并继续驻留
用 法: void keep(int status, int size);
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. Due to the nature of this
function the formula used to compute
the number of paragraphs may not
necessarily work in all cases. Use with
care! Terminate Stay Resident (TSR)
programs are complex and no other support
for them is provided. Refer to the
MS-DOS technical documentation
for more information. */
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/* The clock tick interrupt */
#define INTR 0x1C
/* Screen attribute (blue on grey) */
#define ATTR 0x7900

/* reduce heaplength and stacklength
to make a smaller program in memory */
extern unsigned _heaplen = 1024;
extern unsigned _stklen = 512;

void interrupt ( *oldhandler)(void);

void interrupt handler(void)
{
unsigned int (far *screen)[80];
static int count;

/* For a color screen the video memory
is at B800:0000. For a monochrome
system use B000:000 */
screen = MK_FP(0xB800,0);

/* increase the counter and keep it
within 0 to 9 */
count++;
count %= 10;

/* put the number on the screen */
screen[0][79] = count + '0' + ATTR;

/* call the old interrupt handler */
oldhandler();
}

int main(void)
{

/* get the address of the current clock
tick interrupt */
oldhandler = getvect(INTR);

/* install the new interrupt handler */
setvect(INTR, handler);

/* _psp is the starting address of the
program in memory. The top of the stack
is the end of the program. Using _SS and
_SP together we can get the end of the
stack. You may want to allow a bit of
saftey space to insure that enough room
is being allocated ie:
(_SS + ((_SP + safety space)/16) - _psp)
*/
keep(0, (_SS + (_SP/16) - _psp));
return 0;
}

函数名: labs
用 法: long labs(long n);
程序例:

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int main(void)
{
long result;
long x = -12345678L;

result= labs(x);
printf("number: %ld abs value: %ld\n",
x, result);

return 0;
}

函数名: ldexp
功 能: 计算value*2的幂
用 法: double ldexp(double value, int exp);
程序例:

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int main(void)
{
double value;
double x = 2;

/* ldexp raises 2 by a power of 3
then multiplies the result by 2 */
value = ldexp(x,3);
printf("The ldexp value is: %lf\n",
value);

return 0;
}

函数名: ldiv
功 能: 两个长整型数相除, 返回商和余数
用 法: ldiv_t ldiv(long lnumer, long ldenom);
程序例:

/* ldiv example */

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int main(void)
{
ldiv_t lx;

lx = ldiv(100000L, 30000L);
printf("100000 div 30000 = %ld remainder %ld\n", lx.quot, lx.rem);
return 0;
}

函数名: lfind
功 能: 执行线性搜索
用 法: void *lfind(void *key, void *base, int *nelem, int width,
int (*fcmp)());
程序例:

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int compare(int *x, int *y)
{
return( *x - *y );
}

int main(void)
{
int array[5] = {35, 87, 46, 99, 12};
size_t nelem = 5;
int key;
int *result;

key = 99;
result = lfind(&key, array, &nelem,
sizeof(int), (int(*)(const void *,const void *))compare);
if (result)
printf("Number %d found\n",key);
else
printf("Number %d not found\n",key);

return 0;
}

函数名: line
功 能: 在指定两点间画一直线
用 法: void far line(int x0, int y0, int x1, int y1);
程序例:

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int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;
int xmax, ymax;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
/* an error occurred */
if (errorcode != grOk)
{
printf("Graphics error: %s\n",
grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1);
}

setcolor(getmaxcolor());
xmax = getmaxx();
ymax = getmaxy();

/* draw a diagonal line */
line(0, 0, xmax, ymax);

/* clean up */
getch();
closegraph();
return 0;
}

函数名: linerel
功 能: 从当前位置点(CP)到与CP有一给定相对距离的点画一直线
用 法: void far linerel(int dx, int dy);
程序例:

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int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;
char msg[80];

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk)
{
printf("Graphics error: %s\n",
grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1);
}

/* move the C.P. to location (20, 30) */
moveto(20, 30);

/* create and output a
message at (20, 30) */
sprintf(msg, " (%d, %d)", getx(), gety());
outtextxy(20, 30, msg);

/* draw a line to a point a relative
distance away from the current
value of C.P. */
linerel(100, 100);

/* create and output a message at C.P. */
sprintf(msg, " (%d, %d)", getx(), gety());
outtext(msg);

/* clean up */
getch();
closegraph();
return 0;
}

函数名: localtime
功 能: 把日期和时间转变为结构
用 法: struct tm *localtime(long *clock);
程序例:

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int main(void)
{
time_t timer;
struct tm *tblock;

/* gets time of day */
timer = time(NULL);

/* converts date/time to a structure */
tblock = localtime(&timer);

printf("Local time is: %s", asctime(tblock));

return 0;
}

函数名: lock
功 能: 设置文件共享锁
用 法: int lock(int handle, long offset, long length);
程序例:

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int main(void)
{
int handle, status;
long length;

/* Must have DOS Share.exe loaded for */
/* file locking to function properly */

handle = sopen("c:\\autoexec.bat",
O_RDONLY,SH_DENYNO,S_IREAD);

if (handle < 0)
{
printf("sopen failed\n");
exit(1);
}

length = filelength(handle);
status = lock(handle,0L,length/2);

if (status == 0)
printf("lock succeeded\n");
else
printf("lock failed\n");

status = unlock(handle,0L,length/2);

if (status == 0)
printf("unlock succeeded\n");
else
printf("unlock failed\n");

close(handle);
return 0;
}

函数名: log
功 能: 对数函数ln(x)
用 法: double log(double x);
程序例:

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int main(void)
{
double result;
double x = 8.6872;

result = log(x);
printf("The natural log of %lf is %lf\n", x, result);

return 0;
}

函数名: log10
功 能: 对数函数log
用 法: double log10(double x);
程序例:

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int main(void)
{
double result;
double x = 800.6872;

result = log10(x);
printf("The common log of %lf is %lf\n", x, result);

return 0;
}

函数名: longjump
功 能: 执行非局部转移
用 法: void longjump(jmp_buf env, int val);
程序例:

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void subroutine(jmp_buf);

int main(void)
{

int value;
jmp_buf jumper;

value = setjmp(jumper);
if (value != 0)
{
printf("Longjmp with value %d\n", value);
exit(value);
}
printf("About to call subroutine ... \n");
subroutine(jumper);

return 0;
}

void subroutine(jmp_buf jumper)
{
longjmp(jumper,1);
}

函数名: lowvideo
功 能: 选择低亮度字符
用 法: void lowvideo(void);
程序例:

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int main(void)
{
clrscr();

highvideo();
cprintf("High Intesity Text\r\n");
lowvideo();
gotoxy(1,2);
cprintf("Low Intensity Text\r\n");

return 0;
}

函数名: lrotl, _lrotl
功 能: 将无符号长整型数向左循环移位
用 法: unsigned long lrotl(unsigned long lvalue, int count);
unsigned long _lrotl(unsigned long lvalue, int count);
程序例:

/* lrotl example */
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int main(void)
{
unsigned long result;
unsigned long value = 100;

result = _lrotl(value,1);
printf("The value %lu rotated left one bit is: %lu\n", value, result);

return 0;
}

函数名: lsearch
功 能: 线性搜索
用 法: void *lsearch(const void *key, void *base, size_t *nelem,
size_t width, int (*fcmp)(const void *, const void *));
程序例:

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int compare(int *x, int *y)
{
return( *x - *y );
}

int main(void)
{
int array[5] = {35, 87, 46, 99, 12};
size_t nelem = 5;
int key;
int *result;

key = 99;
result = lfind(&key, array, &nelem,
sizeof(int), (int(*)(const void *,const void *))compare);
if (result)
printf("Number %d found\n",key);
else
printf("Number %d not found\n",key);

return 0;
}

函数名: lseek
功 能: 移动文件读/写指针
用 法: long lseek(int handle, long offset, int fromwhere);
程序例:

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int main(void)
{
int handle;
char msg[] = "This is a test";
char ch;

/* create a file */
handle = open("TEST.$$$", O_CREAT | O_RDWR, S_IREAD | S_IWRITE);

/* write some data to the file */
write(handle, msg, strlen(msg));

/* seek to the begining of the file */
lseek(handle, 0L, SEEK_SET);

/* reads chars from the file until we hit EOF */
do
{
read(handle, &ch, 1);
printf("%c", ch);
} while (!eof(handle));

close(handle);
return 0;
}

main()主函数
每一C 程序都 必须 有一main()函数, 可以根据自己的爱好把它放在程序的某
个地方。有些程序员把它放在最前面, 而另一些程序员把它放在最后面, 无论放
在哪个地方, 以下几点说明都是适合的。
1. main() 参数
在Turbo C2.0启动过程中, 传递main()函数三个参数: argc, argv和env。
* argc: 整数, 为传给main()的命令行参数个数。
* argv: 字符串数组。
在DOS 3.X 版本中, argv[0] 为程序运行的全路径名; 对DOS 3.0
以下的版本, argv[0]为空串("") 。
argv[1] 为在DOS命令行中执行程序名后的第一个字符串;
argv[2] 为执行程序名后的第二个字符串;
...
argv[argc]为NULL。
*env: 安符串数组。env[] 的每一个元素都包含ENVvar=value形式的字符
串。其中ENVvar为环境变量如PATH或87。value 为ENVvar的对应值如C:\DOS, C:
\TURBOC(对于PATH) 或YES(对于87)。
Turbo C2.0启动时总是把这三个参数传递给main()函数, 可以在用户程序中
说明(或不说明)它们, 如果说明了部分(或全部)参数, 它们就成为main()子程序
的局部变量。
请注意: 一旦想说明这些参数, 则必须按argc, argv, env 的顺序, 如以下
的例子:
main()
main(int argc)
main(int argc, char *argv[])
main(int argc, char *argv[], char *env[])
其中第二种情况是合法的, 但不常见, 因为在程序中很少有只用argc, 而不
用argv[]的情况。
以下提供一样例程序EXAMPLE.EXE, 演示如何在main()函数中使用三个参数:
/*program name EXAMPLE.EXE*/
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main(int argc, char *argv[], char *env[])
{
int i;
printf("These are the %d command- line arguments passed to
main:\n\n", argc);
for(i=0; i<=argc; i++)
printf("argv[%d]:%s\n", i, argv[i]);
printf("\nThe environment string(s)on this system are:\n\n");
for(i=0; env[i]!=NULL; i++)
printf(" env[%d]:%s\n", i, env[i]);
}
如果在DOS 提示符下, 按以下方式运行EXAMPLE.EXE:
C:\example first_argument "argument with blanks" 3 4 "last but
one" stop!
注意: 可以用双引号括起内含空格的参数, 如本例中的: " argument
with blanks"和"Last but one")。
结果是这样的:
The value of argc is 7
These are the 7 command-linearguments passed to main:
argv[0]:C:\TURBO\EXAMPLE.EXE
argv[1]:first_argument
argv[2]:argument with blanks
argv[3]:3
argv[4]:4
argv[5]:last but one
argv[6]:stop!
argv[7]:(NULL)
The environment string(s) on this system are:
env[0]: COMSPEC=C:\COMMAND.COM
env[1]: PROMPT=$P$G /*视具体设置而定*/
env[2]: PATH=C:\DOS;C:\TC /*视具体设置而定*/

应该提醒的是: 传送main() 函数的命令行参数的最大长度为128 个字符 (包
括参数间的空格), 这是由DOS 限制的。

函数名: matherr
功 能: 用户可修改的数学错误处理程序
用 法: int matherr(struct exception *e);
程序例:

/* This is a user-defined matherr function that prevents
any error messages from being printed. */

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int matherr(struct exception *a)
{
return 1;
}

函数名: memccpy
功 能: 从源source中拷贝n个字节到目标destin中
用 法: void *memccpy(void *destin, void *source, unsigned char ch,
unsigned n);
程序例:

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int main(void)
{
char *src = "This is the source string";
char dest[50];
char *ptr;

ptr = memccpy(dest, src, 'c', strlen(src));

if (ptr)
{
*ptr = '\0';
printf("The character was found: %s\n", dest);
}
else
printf("The character wasn't found\n");
return 0;
}

函数名: malloc
功 能: 内存分配函数
用 法: void *malloc(unsigned size);
程序例:

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int main(void)
{
char *str;

/* allocate memory for string */
/* This will generate an error when compiling */
/* with C++, use the new operator instead. */
if ((str = malloc(10)) == NULL)
{
printf("Not enough memory to allocate buffer\n");
exit(1); /* terminate program if out of memory */
}

/* copy "Hello" into string */
strcpy(str, "Hello");

/* display string */
printf("String is %s\n", str);

/* free memory */
free(str);

return 0;
}

函数名: memchr
功 能: 在数组的前n个字节中搜索字符
用 法: void *memchr(void *s, char ch, unsigned n);
程序例:

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int main(void)
{
char str[17];
char *ptr;

strcpy(str, "This is a string");
ptr = memchr(str, 'r', strlen(str));
if (ptr)
printf("The character 'r' is at position: %d\n", ptr - str);
else
printf("The character was not found\n");
return 0;
}

函数名: memcpy
功 能: 从源source中拷贝n个字节到目标destin中
用 法: void *memcpy(void *destin, void *source, unsigned n);
程序例:

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int main(void)
{
char src[] = "******************************";
char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";
char *ptr;
printf("destination before memcpy: %s\n", dest);
ptr = memcpy(dest, src, strlen(src));
if (ptr)
printf("destination after memcpy: %s\n", dest);
else
printf("memcpy failed\n");
return 0;
}

函数名: memicmp
功 能: 比较两个串s1和s2的前n个字节, 忽略大小写
用 法: int memicmp(void *s1, void *s2, unsigned n);
程序例:

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int main(void)
{
char *buf1 = "ABCDE123";
char *buf2 = "abcde456";
int stat;
stat = memicmp(buf1, buf2, 5);
printf("The strings to position 5 are ");
if (stat)
printf("not ");
printf("the same\n");
return 0;
}

函数名: memmove
功 能: 移动一块字节
用 法: void *memmove(void *destin, void *source, unsigned n);
程序例:

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int main(void)
{
char *dest = "abcdefghijklmnopqrstuvwxyz0123456789";
char *src = "******************************";
printf("destination prior to memmove: %s\n", dest);
memmove(dest, src, 26);
printf("destination after memmove: %s\n", dest);
return 0;
}

函数名: memset
功 能: 设置s中的所有字节为ch, s数组的大小由n给定
用 法: void *memset(void *s, char ch, unsigned n);
程序例:

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int main(void)
{
char buffer[] = "Hello world\n";

printf("Buffer before memset: %s\n", buffer);
memset(buffer, '*', strlen(buffer) - 1);
printf("Buffer after memset: %s\n", buffer);
return 0;
}

函数名: mkdir
功 能: 建立一个目录
用 法: int mkdir(char *pathname);
程序例:

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int main(void)
{
int status;

clrscr();
status = mkdir("asdfjklm");
(!status) ? (printf("Directory created\n")) :
(printf("Unable to create directory\n"));

getch();
system("dir");
getch();

status = rmdir("asdfjklm");
(!status) ? (printf("Directory deleted\n")) :
(perror("Unable to delete directory"));

return 0;
}