C语言库函数
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()
");
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
", 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
");
getch();
sector = 0;
if (absread(0, 1, sector, &buf) != 0)
{
perror("Disk problem");
exit(1);
}
printf("Read OK
");
strt = 3;
for (i=0; i<80; i++)
{
ch_out = buf[strt+i];
putchar(ch_out);
}
printf("
");
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
",
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
", 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
", segp);
else
printf("Failed: maximum number of paragraphs available is %u
",
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
", 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
", 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
", 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
", 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
", (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
");
} void exit_fn2(void)
{
printf("Exit function #2 called
");
} 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
", 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
", 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
", str, l);
return(0);
}