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POstdio data from write not making it into a file
 

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  1. POstdio data from write not making it into a file
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    <p>I'm having a problem with using stdio commands for manipulating data in a file. I short, when I write data into a file, write returns an int indicating that it was successful, but when I read it back out I only get the old data.</p> <p>Here's a stripped down version of the code:</p> <pre><code>fd = open(filename,O_RDWR|O_APPEND); struct dE *cDE = malloc(sizeof(struct dE)); //Read present data printf("\nreading values at %d\n",off); printf("SeekStatus &lt;%d&gt;\n",lseek(fd,off,SEEK_SET)); printf("ReadStatus &lt;%d&gt;\n",read(fd,cDE,deSize)); printf("current Key/Data &lt;%d/%s&gt;\n",cDE-&gt;key,cDE-&gt;data); printf("\nwriting new values\n"); //Change the values locally cDE-&gt;key = //something new cDE-&gt;data = //something new //Write them back printf("SeekStatus &lt;%d&gt;\n",lseek(fd,off,SEEK_SET)); printf("WriteStatus &lt;%d&gt;\n",write(fd,cDE,deSize)); //Re-read to make sure that it got written back printf("\nre-reading values at %d\n",off); printf("SeekStatus &lt;%d&gt;\n",lseek(fd,off,SEEK_SET)); printf("ReadStatus &lt;%d&gt;\n",read(fd,cDE,deSize)); printf("current Key/Data &lt;%d/%s&gt;\n",cDE-&gt;key,cDE-&gt;data); </code></pre> <p>Furthermore, here's the dE struct in case you're wondering:</p> <pre><code>struct dE { int key; char data[DataSize]; }; </code></pre> <p>This prints:</p> <pre><code>reading values at 1072 SeekStatus &lt;1072&gt; ReadStatus &lt;32&gt; current Key/Data &lt;27/old&gt; writing new values SeekStatus &lt;1072&gt; WriteStatus &lt;32&gt; re-reading values at 1072 SeekStatus &lt;1072&gt; ReadStatus &lt;32&gt; current Key/Data &lt;27/old&gt; </code></pre>
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    1. USdarkpbj
    1. USdarkpbj
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    1. CODoes `read((*fd).fd,cDE,deSize);` compile cleanly? Also, to dereference pointers use `->`, ie `cDE->key`.
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      1. POstdio data from write not making it into a file
      1. USWilliam Morris
    2. COYou never set the values of the variables `offset` and `deSize`, so they might be anything. You never check the return values of `read`, `write`, or `lseek`. You need to post a stripeed down COMPILABLE version of your code that demonstates the problem you are having or the question you are asking. 90% of the time, the excercise of creating that compilable example will answer the question for you.
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      1. POstdio data from write not making it into a file
      1. USChris Dodd
    3. CODo you have permissions on the directory and the file?
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      1. POstdio data from write not making it into a file
      1. UScowboydan
 

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