A开头的函数

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);   }