C语言库函数（C类字母）

2019-11-17 05:00:37

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　　[ 发表日期：2002-1-4 9:28:46 ]

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;
}

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