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); 
} 
  

此C语言函数---A