C语言库函数 (A类字母)

  [ 发表日期:2002-1-4 9:28:46 ]
  函数名: abort
  功 能: 异常终止一个进程
  用 法: void abort(void);
  程序例:
  #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: 确定文件的访问权限
  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: 测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: 注册终止函数
  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);
  }