(持续更新中!!~)22、原来可以这样理解C语言_文件操作(6/8)⽂件的随机读写

目录

 6. ⽂件的随机读写

6.1 fseek

6.2 ftell

6.3 rewind

 6. ⽂件的随机读写

6.1 fseek

        根据⽂件指针的位置和偏移量来定位⽂件指针（⽂件内容的光标）。

int fseek ( FILE * stream, long int offset, int origin );

例⼦：

/* fseek example */
#include <stdio.h>
int main ()
{
    FILE * pFile;
    pFile = fopen ( "example.txt" , "wb" );
    fputs ( "This is an apple." , pFile );
    fseek ( pFile , 9 , SEEK_SET );
    fputs ( " sam" , pFile );
    fclose ( pFile );
return 0;
}

6.2 ftell

返回⽂件指针相对于起始位置的偏移量

long int ftell ( FILE * stream );

例⼦：

/* ftell example : getting size of a file */
#include <stdio.h>
int main ()
{
    FILE * pFile;
    long size;
    pFile = fopen ("myfile.txt","rb");
    if (pFile==NULL)
    perror ("Error opening file");
    else
    {
    fseek (pFile, 0, SEEK_END); // non-portable
    size=ftell (pFile);
    fclose (pFile);
    printf ("Size of myfile.txt: %ld bytes.\n",size);
    }
return 0;
}

6.3 rewind

        让⽂件指针的位置回到⽂件的起始位置

void rewind ( FILE * stream );

例⼦：

/* rewind example */
#include <stdio.h>
int main ()
{
    int n;
    FILE * pFile;
    char buffer [27];
    pFile = fopen ("myfile.txt","w+");
    for ( n='A' ; n<='Z' ; n++)
    fputc ( n, pFile);
    rewind (pFile);
    fread (buffer,1,26,pFile);
    fclose (pFile);
    buffer[26]='\0';
    printf(buffer);
return 0;
}