c语言函数大全(C开头)

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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

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

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

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

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

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

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

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

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

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

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

#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

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

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

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

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

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

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

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

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

#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

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

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

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

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

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

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

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

#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 to quit:\n");

}

return 0;

}