此C语言功能---A

功能名称: abort

动力 能够: 异常终止的过程的

使用 法国: void abort(void);

程序示例:

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
  printf("Calling abort()\n");
  abort();
  return 0; /* This is never reached */
} 

函数名: abs

功 能: 求整数的绝对值

用 法: int abs(int i);

程序例:

#include <stdio.h>
#include <math.h>
int main(void)
{
  int number = -1234;
  printf("number: %d  absolute value: %d\n", number, abs(number));
  return 0;
} 

函数名: absread, abswirte

功 能: 绝对磁盘扇区读、写数据

用 法: int absread(int drive, int nsects, int sectno, void *buffer);

 int abswrite(int drive, int nsects, in tsectno, void *buffer);

程序例:

/* absread example */
#include <stdio.h>
#include <conio.h>
#include <process.h>
#include <dos.h>
int main(void)
{
  int i, strt, ch_out, sector;
  char buf[512];
  printf("Insert a diskette into drive A and press any key\n");
  getch();
  sector = 0;
  if (absread(0, 1, sector, &buf) != 0)
  {
     perror("Disk problem");
     exit(1);
  }
  printf("Read OK\n");
  strt = 3;
  for (i=0; i<80; i++)
  {
     ch_out = buf[strt+i];
     putchar(ch_out);
  }
  printf("\n");
  return(0);
} 

函数名: access

功 能: 确定文件的訪问权限

用 法: int access(const char *filename, int amode);

程序例:

#include <stdio.h>
#include <io.h>
int file_exists(char *filename);
int main(void)
{
  printf("Does NOTEXIST.FIL exist: %s\n",
  file_exists("NOTEXISTS.FIL") ? "YES" : "NO");
  return 0;
}
int file_exists(char *filename)
{
  return (access(filename, 0) == 0);
} 

函数名: acos

功 能: 反余弦函数

用 法: double acos(double x);

程序例:

#include <stdio.h>
#include <math.h>
int main(void)
{
  double result;
  double x = 0.5;
  result = acos(x);
  printf("The arc cosine of %lf is %lf\n", x, result);
  return 0;
} 

函数名: allocmem

功 能: 分配DOS存储段

用 法: int allocmem(unsigned size, unsigned *seg);

程序例:

#include <dos.h>
#include <alloc.h>
#include <stdio.h>
int main(void)
{
  unsigned int size, segp;
  int stat;
  size = 64; /* (64 x 16) = 1024 bytes */
  stat = allocmem(size, &segp);
  if (stat == -1)
     printf("Allocated memory at segment: %x\n", segp);
  else
     printf("Failed: maximum number of paragraphs available is %u\n",
            stat);
  return 0;
} 

函数名: arc

功 能: 画一弧线

用 法: void far arc(int x, int y, int stangle, int endangle, int radius);

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 = 45, endangle = 135;
   int radius = 100;
   /* 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);    /* terminate with an error code */
   }
   midx = getmaxx() / 2;
   midy = getmaxy() / 2;
   setcolor(getmaxcolor());
   /* draw arc */
   arc(midx, midy, stangle, endangle, radius);
   /* clean up */
   getch();
   closegraph();
   return 0;
} 

函数名: asctime

功 能: 转换日期和时间为ASCII码

用 法: char *asctime(const struct tm *tblock);

程序例:

#include <stdio.h>
#include <string.h>
#include <time.h>
int main(void)
{
   struct tm t;
   char str[80];
   /* sample loading of tm structure  */
   t.tm_sec    = 1;  /* Seconds */
   t.tm_min    = 30; /* Minutes */
   t.tm_hour   = 9;  /* Hour */
   t.tm_mday   = 22; /* Day of the Month  */
   t.tm_mon    = 11; /* Month */
   t.tm_year   = 56; /* Year - does not include century */
   t.tm_wday   = 4;  /* Day of the week  */
   t.tm_yday   = 0;  /* Does not show in asctime  */
   t.tm_isdst  = 0;  /* Is Daylight SavTime; does not show in asctime */
   /* converts structure to null terminated
   string */
   strcpy(str, asctime(&t));
   printf("%s\n", str);
   return 0;
} 

函数名: asin

功 能: 反正弦函数

用 法: double asin(double x);

程序例:

#include <stdio.h>
#include <math.h>
int main(void)
{
   double result;
   double x = 0.5;
   result = asin(x);
   printf("The arc sin of %lf is %lf\n", x, result);
   return(0);
} 

函数名: assert

功 能: 測试一个条件并可能使程序终止

用 法: void assert(int test);

程序例:

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
struct ITEM {
   int key;
   int value;
};
/* add item to list, make sure list is not null */
void additem(struct ITEM *itemptr) {
   assert(itemptr != NULL);
   /* add item to list */
}
int main(void)
{
   additem(NULL);
   return 0;
} 

函数名: atan

功 能: 反正切函数

用 法: double atan(double x);

程序例:

#include <stdio.h>
#include <math.h>
int main(void)
{
   double result;
   double x = 0.5;
   result = atan(x);
   printf("The arc tangent of %lf is %lf\n", x, result);
   return(0);
} 

函数名: atan2

功 能: 计算Y/X的反正切值

用 法: double atan2(double y, double x);

程序例:

#include <stdio.h>
#include <math.h>
int main(void)
{
   double result;
   double x = 90.0, y = 45.0;
   result = atan2(y, x);
   printf("The arc tangent ratio of %lf is %lf\n", (y / x), result);
   return 0;
} 

函数名: atexit

功 能: 注冊终止函数

用 法: int atexit(atexit_t func);

程序例:

#include <stdio.h>
#include <stdlib.h>
void exit_fn1(void)
{
   printf("Exit function #1 called\n");
}
void exit_fn2(void)
{
   printf("Exit function #2 called\n");
}
int main(void)
{
   /* post exit function #1 */
   atexit(exit_fn1);
   /* post exit function #2 */
   atexit(exit_fn2);
   return 0;
} 

函数名: atof

功 能: 把字符串转换成浮点数

用 法: double atof(const char *nptr);

程序例:

#include <stdlib.h>
#include <stdio.h>
int main(void)
{
   float f;
   char *str = "12345.67";
   f = atof(str);
   printf("string = %s float = %f\n", str, f);
   return 0;
} 

函数名: atoi

功 能: 把字符串转换成长整型数

用 法: int atoi(const char *nptr);

程序例:

#include <stdlib.h>
#include <stdio.h>
int main(void)
{
   int n;
   char *str = "12345.67";
   n = atoi(str);
   printf("string = %s integer = %d\n", str, n);
   return 0;
} 

函数名: atol

功 能: 把字符串转换成长整型数

用 法: long atol(const char *nptr);

程序例:

#include <stdlib.h>
#include <stdio.h>
int main(void)
{
   long l;
   char *str = "98765432";
   l = atol(lstr);
   printf("string = %s integer = %ld\n", str, l);
   return(0);
} 

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