fread,fwrite ,fscanf,fprintf 使用 @ 自由手記

函數名: fread
功能: 從一個流中讀數據
用法: int fread(void*ptr, int size, int nitems, FILE *stream);
程序例:

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

int main(void)
{
   FILE *stream;
   char msg[] ="this is a test";
   char buf[20];

   if ((stream = fopen("DUMMY.FIL", "w+"))
       == NULL)
   {
      fprintf(stderr,
              "Cannot open output file.\n");
      return1;
   }

   /* write some data to the file */
   fwrite(msg, strlen(msg)+1, 1, stream);

   /* seek to the beginning of the file */
   fseek(stream, SEEK_SET, 0);

   /* read the data and display it */
   fread(buf, strlen(msg)+1, 1, stream);
   printf("%s\n", buf);

   fclose(stream);
   return0;
}

C/C++ code

函數名: fwrite
功能: 寫內容到流中
用法: int fwrite(void*ptr, int size, int nitems, FILE *stream);
程序例:

#include <stdio.h>

struct mystruct
{
int i;
char ch;
};

int main(void)
{
FILE *stream;
struct mystruct s;

if ((stream = fopen("TEST.$$$", "wb")) == NULL) /* open file TEST.$$$ */
{
fprintf(stderr, "Cannot open output file.\n");
return1;
}
s.i =0;
s.ch ='A';
fwrite(&s, sizeof(s), 1, stream); /* write struct s to file */
fclose(stream); /* close file */
return0;
}

函數名: fscanf
功能: 從一個流中執行格式化輸入
用法: int fscanf(FILE *stream, char*format[,argument...]);
程序例:

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

int main(void)
{
int i;

printf("Input an integer: ");

/* read an integer from the
standard input stream */
if (fscanf(stdin, "%d", &i))
printf("The integer read was: %i\n",
i);
else
{
fprintf(stderr, "Error reading an \
integer from stdin.\n");
exit(1);
}
return0;
}

C/C++ code: 函數名: fprintf
功能: 傳送格式化輸出到一個流中
用法: int fprintf(FILE *stream, char*format[, argument,...]);
程序例:

/* Program to create backup of the
AUTOEXEC.BAT file */

#include <stdio.h>

int main(void)
{
FILE *in, *out;

if ((in= fopen("\\AUTOEXEC.BAT", "rt"))
== NULL)
{
fprintf(stderr, "Cannot open input \
file.\n");
return1;
}

if ((out= fopen("\\AUTOEXEC.BAK", "wt"))
== NULL)
{
fprintf(stderr, "Cannot open output \
file.\n");
return1;
}

while (!feof(in))
fputc(fgetc(in), out);

fclose(in);
fclose(out);
return0;
}