《C语言函数速查》A开头的函数

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内容导航：

• 01、abort
• 02、abs
• 03、absread
• 04、abswirte
• 05、access
• 06、acos
• 07、allocmem
• 08、arc
• 09、asctime
• 10、asin
• 11、assert
• 12、atan
• 13、atan2
• 14、atexit
• 15、atof
• 16、atoi
• 17、atol

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01、abort

函数名: abort
功能: 异常终止一个进程
用法: void abort(void);
示例代码:

#include 
#include 

int main(void)
{
  printf("Calling abort()\n");
  abort();
  return 0; /* This is never reached */
}

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02、abs

函数名: abs
功能: 求整数的绝对值
用法: int abs(int i);
示例代码:

#include 
#include 

int main(void)
{
  int number = -1234;

  printf("number: %d  absolute value: %d\n", number, abs(number));
  return 0;
}

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03、absread

函数名: absread
功能: 绝对磁盘扇区读数据
用法: int absread(int drive, int nsects, int sectno, void *buffer);
示例代码：

--

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04、abswirte

函数名: abswirte
功能: 绝对磁盘扇区写数据
用法: int abswrite(int drive, int nsects, in tsectno, void *buffer);
示例代码：

/* absread example */

#include 
#include 
#include 
#include 

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);
}

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05、access

函数名: access
功能: 确定文件的访问权限
用法: int access(const char *filename, int amode);
示例代码:

#include 
#include 

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);
}

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06、acos

函数名: acos
功能: 反余弦函数
用法: double acos(double x);
示例代码:

#include 
#include 

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;
}

---

07、allocmem

函数名: allocmem
功能: 分配DOS存储段
用法: int allocmem(unsigned size, unsigned *seg);
示例代码:

#include 
#include 
#include 

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;
}

---

08、arc

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);
示例代码:

#include 
#include 
#include 
#include 

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;
}

---

09、asctime

函数名: asctime
功能: 转换日期和时间为ASCII码
用法: char *asctime(const struct tm *tblock);
示例代码:

#include 
#include 
#include 

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;
}

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10、asin

函数名: asin
功能: 反正弦函数
用法: double asin(double x);
示例代码:

#include 
#include 

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);
}

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11、assert

函数名: assert
功能: 测试一个条件并可能使程序终止
用法: void assert(int test);
示例代码:

#include 
#include 
#include 

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;
}

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12、atan

函数名: atan
功能: 反正切函数
用法: double atan(double x);
示例代码:

#include 
#include 

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);
}

---

13、atan2

函数名: atan2
功能: 计算Y/X的反正切值
用法: double atan2(double y, double x);
示例代码:

#include 
#include 

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;
}

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14、atexit

函数名: atexit
功能: 注册终止函数
用法: int atexit(atexit_t func);
示例代码:

#include 
#include 

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;
}

---

15、atof

函数名: atof
功能: 把字符串转换成浮点数
用法: double atof(const char *nptr);
示例代码:

#include 
#include 

int main(void)
{
   float f;
   char *str = "12345.67";

   f = atof(str);
   printf("string = %s float = %f\n", str, f);
   return 0;
}

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16、atoi

函数名: atoi
功能: 把字符串转换成长整型数
用法: int atoi(const char *nptr);
示例代码:

#include 
#include 

int main(void)
{
   int n;
   char *str = "12345.67";

   n = atoi(str);
   printf("string = %s integer = %d\n", str, n);
   return 0;
}

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17、atol

函数名: atol
功能: 把字符串转换成长整型数
用法: long atol(const char *nptr);
示例代码:

#include 
#include 

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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