C开头的函数

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;   }