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C语言教程C语言函数: R

C语言函数: R

更新时间:2013-03-25 12:55:12 |

函数名: raise
功  能: 向正在执行的程序发送一个信号
用  法: int raise(int sig);
程序例:

#include <signal.h>

int main(void)
{
   int a, b;

   a = 10;
   b = 0;
   if (b == 0)
   /* preempt divide by zero error */
      raise(SIGFPE);
   a = a / b;
   return 0;
}
 
 

函数名: rand
功  能: 随机数发生器
用  法: void rand(void);
程序例:

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

int main(void)
{
   int i;

   printf("Ten random numbers from 0 to 99\n\n");
   for(i=0; i<10; i++)
      printf("%d\n", rand() % 100);
   return 0;
}
 
 

函数名: randbrd
功  能: 随机块读
用  法: int randbrd(struct fcb *fcbptr, int reccnt);
程序例:

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

int main(void)
{
   char far *save_dta;
   char line[80], buffer[256];
   struct fcb blk;
   int i, result;

   /* get user input file name for dta */
   printf("Enter drive and file name (no path - i.e. a:file.dat)\n");
   gets(line);

   /* put file name in fcb */
   if (!parsfnm(line, &blk, 1))
   {
      printf("Error in call to parsfnm\n");
      exit(1);
   }
   printf("Drive #%d  File: %s\n\n", blk.fcb_drive, blk.fcb_name);

   /* open file with DOS FCB open file */
   bdosptr(0x0F, &blk, 0);

   /* save old dta, and set new one */
   save_dta = getdta();
   setdta(buffer);

   /* set up info for the new dta */
   blk.fcb_recsize = 128;
   blk.fcb_random = 0L;
   result = randbrd(&blk, 1);

   /* check results from randbrd */
   if (!result)
      printf("Read OK\n\n");
   else
   {
      perror("Error during read");
      exit(1);
   }

   /* read in data from the new dta */
   printf("The first 128 characters are:\n");
   for (i=0; i<128; i++)
      putchar(buffer[i]);

   /* restore previous dta */
   setdta(save_dta);

   return 0;
}
 

函数名: randbwr
功  能: 随机块写
用  法: int randbwr(struct fcp *fcbptr, int reccnt);
程序例:

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

int main(void)
{
   char far *save_dta;
   char line[80];
   char buffer[256] = "RANDBWR test!";
   struct fcb blk;
   int result;

   /* get new file name from user */
   printf("Enter a file name to create (no path - ie. a:file.dat\n");
   gets(line);

   /* parse the new file name to the dta */
   parsfnm(line,&blk,1);
   printf("Drive #%d  File: %s\n", blk.fcb_drive, blk.fcb_name);

   /* request DOS services to create file */
   if (bdosptr(0x16, &blk, 0) == -1)
   {
      perror("Error creating file");
      exit(1);
   }

   /* save old dta and set new dta */
   save_dta = getdta();
   setdta(buffer);

   /* write new records */
   blk.fcb_recsize = 256;
   blk.fcb_random = 0L;
   result = randbwr(&blk, 1);

   if (!result)
      printf("Write OK\n");
   else
   {
      perror("Disk error");
      exit(1);
   }

   /* request DOS services to close the file */
   if (bdosptr(0x10, &blk, 0) == -1)
   {
      perror("Error closing file");
      exit(1);
   }

   /* reset the old dta */
   setdta(save_dta);

   return 0;
}
 
 

函数名: random
功  能: 随机数发生器
用  法: int random(int num);
程序例:

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

/* prints a random number in the range 0 to 99 */
int main(void)
{
   randomize();
   printf("Random number in the 0-99 range: %d\n", random (100));
   return 0;
}
 
 

函数名: randomize
功  能: 初始化随机数发生器
用  法: void randomize(void);
程序例:

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

int main(void)
{
   int i;

   randomize();
   printf("Ten random numbers from 0 to 99\n\n");
   for(i=0; i<10; i++)
       printf("%d\n", rand() % 100);
   return 0;
}
 
 

函数名: read
功  能: 从文件中读
用  法: int read(int handle, void *buf, int nbyte);
程序例:

#include <stdio.h>
#include <io.h>
#include <alloc.h>
#include <fcntl.h>
#include <process.h>
#include <sys\stat.h>

int main(void)
{
   void *buf;
   int handle, bytes;

   buf = malloc(10);

/*
   Looks for a file in the current directory named TEST.$$$ and attempts
   to read 10 bytes from it.  To use this example you should create the
   file TEST.$$$
*/
   if ((handle =
      open("TEST.$$$", O_RDONLY | O_BINARY, S_IWRITE | S_IREAD)) == -1)
   {
      printf("Error Opening File\n");
      exit(1);
   }

   if ((bytes = read(handle, buf, 10)) == -1) {
      printf("Read Failed.\n");
      exit(1);
   }
   else {
      printf("Read: %d bytes read.\n", bytes);
   }
   return 0;
}
 
 

函数名: realloc
功  能: 重新分配主存
用  法: void *realloc(void *ptr, unsigned newsize);
程序例:

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

int main(void)
{
   char *str;

   /* allocate memory for string */
   str = malloc(10);

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

   printf("String is %s\n  Address is %p\n", str, str);
   str = realloc(str, 20);
   printf("String is %s\n  New address is %p\n", str, str);

   /* free memory */
   free(str);

   return 0;
}
 
 

函数名: rectangle
功  能: 画一个矩形
用  法: void far rectangle(int left, int top, int right, int bottom);
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 left, top, right, bottom;

   /* 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 */
   }

   left = getmaxx() / 2 - 50;
   top = getmaxy() / 2 - 50;
   right = getmaxx() / 2 + 50;
   bottom = getmaxy() / 2 + 50;

   /* draw a rectangle */
   rectangle(left,top,right,bottom);

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

函数名: registerbgidriver
功  能: 登录已连接进来的图形驱动程序代码
用  法: int registerbgidriver(void(*driver)(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;

   /* register a driver that was added into graphics.lib */
   errorcode = registerbgidriver(EGAVGA_driver);

   /* report any registration errors */
   if (errorcode < 0)
   {
      printf("Graphics error: %s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1); /* terminate with an error code */
   }

   /* 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 */
   }

   /* draw a line */
   line(0, 0, getmaxx(), getmaxy());

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

函数名: remove
功  能: 删除一个文件
用  法: int remove(char *filename);
程序例:

#include <stdio.h>

int main(void)
{
   char file[80];

   /* prompt for file name to delete */
   printf("File to delete: ");
   gets(file);

   /* delete the file */
   if (remove(file) == 0)
      printf("Removed %s.\n",file);
   else
      perror("remove");

   return 0;
}
 
 

函数名: rename
功  能: 重命名文件
用  法: int rename(char *oldname, char *newname);
程序例:

#include <stdio.h>

int main(void)
{
   char oldname[80], newname[80];

   /* prompt for file to rename and new name */
   printf("File to rename: ");
   gets(oldname);
   printf("New name: ");
   gets(newname);

   /* Rename the file */
   if (rename(oldname, newname) == 0)
      printf("Renamed %s to %s.\n", oldname, newname);
   else
      perror("rename");

   return 0;
}
 
 

函数名: restorecrtmode
功  能: 将屏幕模式恢复为先前的imitgraph设置
用  法: void far restorecrtmode(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 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 */
   }

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

   /* output a message */
   settextjustify(CENTER_TEXT, CENTER_TEXT);
   outtextxy(x, y, "Press any key to exit graphics:");
   getch();

   /* restore system to text mode */
   restorecrtmode();
   printf("We're now in text mode.\n");
   printf("Press any key to return to graphics mode:");
   getch();

   /* return to graphics mode */
   setgraphmode(getgraphmode());

   /* output a message */
   settextjustify(CENTER_TEXT, CENTER_TEXT);
   outtextxy(x, y, "We're back in graphics mode.");
   outtextxy(x, y+textheight("W"), "Press any key to halt:");

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

函数名: rewind
功  能: 将文件指针重新指向一个流的开头
用  法: int rewind(FILE *stream);
程序例:

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

 int main(void)
 {
    FILE *fp;
    char *fname = "TXXXXXX", *newname, first;

    newname = mktemp(fname);
    fp = fopen(newname,"w+");
    fprintf(fp,"abcdefghijklmnopqrstuvwxyz");
    rewind(fp);
    fscanf(fp,"%c",&first);
    printf("The first character is: %c\n",first);
    fclose(fp);
    remove(newname);

    return 0;
}
 
 

函数名: rmdir
功  能: 删除DOS文件目录
用  法: int rmdir(char *stream);
程序例:

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

#define DIRNAME "testdir.$$$"

int main(void)
{
   int stat;

   stat = mkdir(DIRNAME);
   if (!stat)
          printf("Directory created\n");
   else
   {
      printf("Unable to create directory\n");
      exit(1);
   }

   getch();
   system("dir/p");
   getch();

   stat = rmdir(DIRNAME);
   if (!stat)
          printf("\nDirectory deleted\n");
   else
   {
   perror("\nUnable to delete directory\n");
      exit(1);
   }

   return 0;
}

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