fseek Linux 编程手册

骑猪看日落 2022-06-07 23:46 162阅读 0赞

#include <stdio.h>
    #include <stdlib.h>
     
    int main(void)
    {
        /* Prepare an array of f-p values. */
        #define SIZE 5
        double A[SIZE] = {1.,2.,3.,4.,5.};
        /* Write array to a file. */
        FILE * fp = fopen("test.bin", "wb");
        fwrite(A,sizeof(double),SIZE,fp);
        fclose (fp);
     
        /* Read the f-p values into array B. */
        double B[SIZE];
        fp = fopen("test.bin","rb");
     
        /* Set the file position indicator in front of third f-p value. */
        if (fseek(fp,sizeof(double)*3L,SEEK_SET) != 0)
        {
           if (ferror(fp))
           {
              perror("fseek()");
              fprintf(stderr,"fseek() failed in file %s at line # %d\n", __FILE__,__LINE__-5);
              exit(EXIT_FAILURE);
           }
        }
     
        int ret_code = fread(B,sizeof(double),1,fp);   /* read one f-p value  */
        printf("%.1f\n", B[0]);                        /* print one f-p value */
     
        fclose(fp);
        return EXIT_SUCCESS;
    }

结果输出

4.0

fseek参数解释

<table style="font-size:12.8px; border-spacing:0px; color:rgb(0,0,0); font-family:DejaVuSans,&quot;DejaVu Sans&quot;,arial,sans-serif"> 
 <tbody> 
  <tr> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top; white-space:nowrap; text-align:right; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> stream</td> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top">-</td> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top; width:674.542px">file stream to modify 将要改变的文件流</td> 
  </tr> 
  <tr> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top; white-space:nowrap; text-align:right; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> offset</td> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top">-</td> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top; width:674.542px">number of characters to shift the position relative to origin 相对于origin 位置偏移的字符个数</td> 
  </tr> 
  <tr> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top; white-space:nowrap; text-align:right; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> origin</td> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top">-</td> 
   <td style="padding:0.5em 1em 0px 0px; vertical-align:top; width:674.542px">position to which&nbsp;<code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent">offset</code>&nbsp;is added. It can have one of the following values:&nbsp;<span style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important"><a href="http://en.cppreference.com/w/c/io" title="c/io" style="color:rgb(11,0,128); background:none" rel="nofollow">SEEK_SET</a></span>,&nbsp;<span style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important"><a href="http://en.cppreference.com/w/c/io" title="c/io" style="color:rgb(11,0,128); background:none" rel="nofollow">SEEK_CUR</a></span>,&nbsp;<span style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important"><a href="http://en.cppreference.com/w/c/io" title="c/io" style="color:rgb(11,0,128); background:none" rel="nofollow">SEEK_END</a>位置信息：开始，当前以及结尾</span></td> 
  </tr> 
 </tbody> 
</table>