C语言库函数(C类字母)

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C语言库函数(C类字母)


函数名: cabs
功 能: 计算复数的绝对值
用 法: double cabs(struct complex z);
程序例:
#include <stdio.h>
#include <math.h>

int main(void)
{
struct complex z;
double val;

z.x = 2.0;
z.y = 1.0;
val = cabs(z);

printf("The absolute value of %.2lfi %.2lfj is %.2lf", z.x, z.y, val);
return 0;
}




函数名: calloc
功 能: 分配主存储器
用 法: void *calloc(size_t nelem, size_t elsize);
程序例:

#include <stdio.h>
#include <alloc.h>

int main(void)
{
char *str = NULL;

/* allocate memory for string */
str = calloc(10, sizeof(char));

/* copy "Hello" into string */
strcpy(str, "Hello");

/* display string */
printf("String is %s\n", str);

/* free memory */
free(str);

return 0;
}




函数名: ceil
功 能: 向上舍入
用 法: double ceil(double x);
程序例:

#include <math.h>
#include <stdio.h>

int main(void)
{
double number = 123.54;
double down, up;

down = floor(number);
up = ceil(number);

printf("original number %5.2lf\n", number);
printf("number rounded down %5.2lf\n", down);
printf("number rounded up %5.2lf\n", up);

return 0;
}




函数名: cgets
功 能: 从控制台读字符串
用 法: char *cgets(char *str);
程序例:

#include <stdio.h>
#include <conio.h>

int main(void)
{
char buffer[83];
char *p;

/* There's space for 80 characters plus the NULL terminator */
buffer[0] = 81;

printf("Input some chars:");
p = cgets(buffer);
printf("\ncgets read %d characters: \"%s\"\n", buffer[1], p);
printf("The returned pointer is %p, buffer[0] is at %p\n", p, &buffer);

/* Leave room for 5 characters plus the NULL terminator */
buffer[0] = 6;

printf("Input some chars:");
p = cgets(buffer);
printf("\ncgets read %d characters: \"%s\"\n", buffer[1], p);
printf("The returned pointer is %p, buffer[0] is at %p\n", p, &buffer);
return 0;
}




函数名: chdir
功 能: 改变工作目录
用 法: int chdir(const char *path);
程序例:

#include <stdio.h>
#include <stdlib.h>
#include <dir.h>

char old_dir[MAXDIR];
char new_dir[MAXDIR];

int main(void)
{
if (getcurdir(0, old_dir))
{
perror("getcurdir()");
exit(1);
}
printf("Current directory is: \\%s\n", old_dir);

if (chdir("\\"))
{
perror("chdir()");
exit(1);
}

if (getcurdir(0, new_dir))
{
perror("getcurdir()");
exit(1);
}
printf("Current directory is now: \\%s\n", new_dir);

printf("\nChanging back to orignal directory: \\%s\n", old_dir);
if (chdir(old_dir))
{
perror("chdir()");
exit(1);
}

return 0;
}



函数名: _chmod, chmod
功 能: 改变文件的访问方式
用 法: int chmod(const char *filename, int permiss);
程序例:

#include <sys\stat.h>
#include <stdio.h>
#include <io.h>

void make_read_only(char *filename);

int main(void)
{
make_read_only("NOTEXIST.FIL");
make_read_only("MYFILE.FIL");
return 0;
}

void make_read_only(char *filename)
{
int stat;

stat = chmod(filename, S_IREAD);
if (stat)
printf("Couldn't make %s read-only\n", filename);
else
printf("Made %s read-only\n", filename);
}




函数名: chsize
功 能: 改变文件大小
用 法: int chsize(int handle, long size);
程序例:

#include <string.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
int handle;
char buf[11] = "0123456789";

/* create text file containing 10 bytes */
handle = open("DUMMY.FIL", O_CREAT);
write(handle, buf, strlen(buf));

/* truncate the file to 5 bytes in size */
chsize(handle, 5);

/* close the file */
close(handle);
return 0;
}



函数名: circle
功 能: 在给定半径以(x, y)为圆心画圆
用 法: void far circle(int x, int y, 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 radius = 100;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
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 the circle */
circle(midx, midy, radius);

/* clean up */
getch();
closegraph();
return 0;
}




函数名: cleardevice
功 能: 清除图形屏幕
用 法: void far cleardevice(void);
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;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
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());

/* for centering screen messages */
settextjustify(CENTER_TEXT, CENTER_TEXT);

/* output a message to the screen */
outtextxy(midx, midy, "press any key to clear the screen:");

/* wait for a key */
getch();

/* clear the screen */
cleardevice();

/* output another message */
outtextxy(midx, midy, "press any key to quit:");

/* clean up */
getch();
closegraph();
return 0;
}




函数名: clearerr
功 能: 复位错误标志
用 法:void clearerr(FILE *stream);
程序例:

#include <stdio.h>

int main(void)
{
FILE *fp;
char ch;

/* open a file for writing */
fp = fopen("DUMMY.FIL", "w");

/* force an error condition by attempting to read */
ch = fgetc(fp);
printf("%c\n",ch);

if (ferror(fp))
{
/* display an error message */
printf("Error reading from DUMMY.FIL\n");

/* reset the error and EOF indicators */
clearerr(fp);
}

fclose(fp);
return 0;
}




函数名: clearviewport
功 能: 清除图形视区
用 法: void far clearviewport(void);
程序例:

#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>

#define CLIP_ON 1 /* activates clipping in viewport */

int main(void)
{
/* request auto detection */
int gdriver = DETECT, gmode, errorcode;
int ht;

/* initialize graphics and local variables */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();
if (errorcode != grOk) /* an error occurred */
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

setcolor(getmaxcolor());
ht = textheight("W");

/* message in default full-screen viewport */
outtextxy(0, 0, "* <-- (0, 0) in default viewport");

/* create a smaller viewport */
setviewport(50, 50, getmaxx()-50, getmaxy()-50, CLIP_ON);

/* display some messages */
outtextxy(0, 0, "* <-- (0, 0) in smaller viewport");
outtextxy(0, 2*ht, "Press any key to clear viewport:");

/* wait for a key */
getch();

/* clear the viewport */
clearviewport();

/* output another message */
outtextxy(0, 0, "Press any key to quit:");

/* clean up */
getch();
closegraph();
return 0;
}




函数名: _close, close
功 能: 关闭文件句柄
用 法: int close(int handle);
程序例:

#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>

main()
{
int handle;
char buf[11] = "0123456789";

/* create a file containing 10 bytes */
handle = open("NEW.FIL", O_CREAT);
if (handle > -1)
{
write(handle, buf, strlen(buf));

/* close the file */
close(handle);
}
else
{
printf("Error opening file\n");
}
return 0;
}




函数名: clock
功 能: 确定处理器时间
用 法: clock_t clock(void);
程序例:

#include <time.h>
#include <stdio.h>
#include <dos.h>

int main(void)
{
clock_t start, end;
start = clock();

delay(2000);

end = clock();
printf("The time was: %f\n", (end - start) / CLK_TCK);

return 0;
}




函数名: closegraph
功 能: 关闭图形系统
用 法: void far closegraph(void);
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 x, y;

/* initialize graphics mode */
initgraph(&gdriver, &gmode, "");

/* read result of initialization */
errorcode = graphresult();

if (errorcode != grOk) /* an error
occurred */
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1); /* terminate with an error code */
}

x = getmaxx() / 2;
y = getmaxy() / 2;

/* output a message */
settextjustify(CENTER_TEXT, CENTER_TEXT);
outtextxy(x, y, "Press a key to close the graphics system:");

/* wait for a key */
getch();

/* closes down the graphics system */
closegraph();

printf("We're now back in text mode.\n");
printf("Press any key to halt:");
getch();
return 0;
}




函数名: clreol
功 能: 在文本窗口中清除字符到行末
用 法: void clreol(void);
程序例:

#include <conio.h>

int main(void)

{
clrscr();
cprintf("The function CLREOL clears all characters from the\r\n");
cprintf("cursor position to the end of the line within the\r\n");
cprintf("current text window, without moving the cursor.\r\n");
cprintf("Press any key to continue . . .");
gotoxy(14, 4);
getch();

clreol();
getch();

return 0;
}




函数名: clrscr
功 能: 清除文本模式窗口
用 法: void clrscr(void);
程序例:

#include <conio.h>

int main(void)
{
int i;

clrscr();
for (i = 0; i < 20; i++)
cprintf("%d\r\n", i);
cprintf("\r\nPress any key to clear screen");
getch();

clrscr();
cprintf("The screen has been cleared!");
getch();

return 0;
}




函数名: coreleft
功 能: 返回未使用内存的大小
用 法: unsigned coreleft(void);
程序例:

#include <stdio.h>
#include <alloc.h>

int main(void)
{
printf("The difference between the highest allocated block and\n");
printf("the top of the heap is: %lu bytes\n", (unsigned long) coreleft());

return 0;
}


函数名: cos
功 能: 余弦函数
用 法: double cos(double x);
程序例:

#include <stdio.h>
#include <math.h>

int main(void)
{
double result;
double x = 0.5;

result = cos(x);
printf("The cosine of %lf is %lf\n", x, result);
return 0;
}




函数名: cosh
功 能: 双曲余弦函数
用 法: dluble cosh(double x);
程序例:

#include <stdio.h>
#include <math.h>

int main(void)
{
double result;
double x = 0.5;

result = cosh(x);
printf("The hyperboic cosine of %lf is %lf\n", x, result);
return 0;
}




函数名: country
功 能: 返回与国家有关的信息
用 法: struct COUNTRY *country(int countrycode, struct country *country);
程序例:

#include <dos.h>
#include <stdio.h>

#define USA 0

int main(void)
{
struct COUNTRY country_info;

country(USA, &country_info);
printf("The currency symbol for the USA is: %s\n",
country_info.co_curr);
return 0;
}




函数名: cprintf
功 能: 送格式化输出至屏幕
用 法: int cprintf(const char *format[, argument, ...]);
程序例:

#include <conio.h>

int main(void)
{
/* clear the screen */
clrscr();

/* create a text window */
window(10, 10, 80, 25);

/* output some text in the window */
cprintf("Hello world\r\n");

/* wait for a key */
getch();
return 0;
}




函数名: cputs
功 能: 写字符到屏幕
用 法: void cputs(const char *string);
程序例:

#include <conio.h>

int main(void)
{
/* clear the screen */
clrscr();

/* create a text window */
window(10, 10, 80, 25);

/* output some text in the window */
cputs("This is within the window\r\n");

/* wait for a key */
getch();
return 0;
}




函数名: _creat creat
功 能: 创建一个新文件或重写一个已存在的文件
用 法: int creat (const char *filename, int permiss);
程序例:

#include <sys\stat.h>
#include <string.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
int handle;
char buf[11] = "0123456789";

/* change the default file mode from text to binary */
_fmode = O_BINARY;

/* create a binary file for reading and writing */
handle = creat("DUMMY.FIL", S_IREAD | S_IWRITE);

/* write 10 bytes to the file */
write(handle, buf, strlen(buf));

/* close the file */
close(handle);
return 0;
}


函数名: creatnew
功 能: 创建一个新文件
用 法: int creatnew(const char *filename, int attrib);
程序例:

#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <dos.h>
#include <io.h>

int main(void)
{
int handle;
char buf[11] = "0123456789";

/* attempt to create a file that doesn't already exist */
handle = creatnew("DUMMY.FIL", 0);

if (handle == -1)
printf("DUMMY.FIL already exists.\n");
else
{
printf("DUMMY.FIL successfully created.\n");
write(handle, buf, strlen(buf));
close(handle);
}
return 0;
}




函数名: creattemp
功 能: 创建一个新文件或重写一个已存在的文件
用 法: int creattemp(const char *filename, int attrib);
程序例:

#include <string.h>
#include <stdio.h>
#include <io.h>

int main(void)
{
int handle;
char pathname[128];

strcpy(pathname, "\\");

/* create a unique file in the root directory */
handle = creattemp(pathname, 0);

printf("%s was the unique file created.\n", pathname);
close(handle);
return 0;
}




函数名: cscanf
功 能: 从控制台执行格式化输入
用 法: int cscanf(char *format[,argument, ...]);
程序例:

#include <conio.h>

int main(void)
{
char string[80];

/* clear the screen */
clrscr();

/* Prompt the user for input */
cprintf("Enter a string with no spaces:");

/* read the input */
cscanf("%s", string);

/* display what was read */
cprintf("\r\nThe string entered is: %s", string);
return 0;
}




函数名: ctime
功 能: 把日期和时间转换为字符串
用 法: char *ctime(const time_t *time);
程序例:

#include <stdio.h>
#include <time.h>

int main(void)
{
time_t t;

time(&t);
printf("Today's date and time: %s\n", ctime(&t));
return 0;
}




函数名: ctrlbrk
功 能: 设置Ctrl-Break处理程序
用 法: void ctrlbrk(*fptr)(void);
程序例:

#include <stdio.h>
#include <dos.h>

#define ABORT 0

int c_break(void)
{
printf("Control-Break pressed. Program aborting ...\n");
return (ABORT);
}

int main(void)
{
ctrlbrk(c_break);
for(;;)
{
printf("Looping... Press <Ctrl-Break> to quit:\n");
}
return 0;
}