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POUnexpected behavior while creating, writing and reading a Random Access File in C
 

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  1. POUnexpected behavior while creating, writing and reading a Random Access File in C
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    <p>I have been dealing with a problem with 3 programs from this book: <a href="http://rads.stackoverflow.com/amzn/click/0136123562" rel="nofollow noreferrer">C How to Program - Deitel</a> They are related to the chapter 11 managing Files (Sequential and random access Files) in my studying method I like to test the example programs before I head the exercises, and I couldn't make work the 3 examples of the random access files (creating, reading and writing) I have got three unexpected behaviors. let me show:</p> <ul> <li><p>First I run the random access file creator, nothing seems weird and I get the finish message. <img src="https://i.stack.imgur.com/GkzXi.png" alt="enter image description here"></p></li> <li><p>Second I compile the writing random access values file, then enter the values, nothing seems weird. <img src="https://i.stack.imgur.com/96TjP.png" alt="Entering values"></p></li> <li><p>Third I want to use the hare strategy and read the .dat file with notepad to see if the data got saved properly. And surprise some garbage is showed. And i thought well, maybe the double representation doesn't match with the reading program (notepad). So i moved to the fourth step.</p></li> </ul> <p><img src="https://i.stack.imgur.com/s1dgk.png" alt="Reading File notepad"></p> <ul> <li><p>Fourth I compile the reading random access files program. and surprise the data showed isn't what I entered.</p> <p><img src="https://i.stack.imgur.com/V7LT7.png" alt="results didn&#39;t match"></p></li> </ul> <p>I didn't want to post this question here cause I know there are more important questions, and more interesting but i can't find what I did wrong, and I have been looking for some time and I finally decided to ask the experts. I leave you the SC below (Thanks!):</p> <pre><code>/*To create the file*/ #include &lt;stdio.h&gt; struct clientsData{ int account; char lastname[ 30 ], name[ 30 ]; double balance; }; int main(void) { int i; struct clientsData client = { 0, "", "", 0.0 }; FILE *cfPtr; if( ( cfPtr = fopen( "clients.dat", "wb" ) ) == NULL ) { printf( "File couldn't be opened. " ); } else{ printf( "Generating\n" ); for ( i = 1; i &lt;= 10000; i++ ){ printf( "-" ); fwrite( &amp;client, sizeof( struct clientsData ), 1, cfPtr ); } fclose( cfPtr ); } printf( "\nFile succesfully created\n" ); return 0; } </code></pre> <hr> <pre><code>/* To write the file */ #include &lt;stdio.h&gt; struct clientsData{ int account; char lastname[ 30 ], name[ 30 ]; double balance; }; int main(void) { FILE *cfPtr; struct clientsData client = { 0, "", "", 0.0 }; if( ( cfPtr = fopen( "clients.dat", "rb+" ) ) == NULL ) { printf( "File couldn't be opened. " ); } else{ printf( "Enter account number"" ( 1 to 10000, 0 to end the input )\n?" ); scanf( "%d", &amp;client.account ); while( client.account != 0 ){ printf( "Enter the lastname, firstname and the balance\n?" ); fscanf( stdin, "%s%s%lf", client.lastname, client.name, &amp;client.balance ); fseek( cfPtr, ( client.account - 1 ) * sizeof( struct clientsData ), SEEK_SET ); fwrite( &amp;client, sizeof( struct clientsData ), 1, cfPtr ); printf( "Enter account number\n?" ); scanf( "%d", &amp;client.account ); } fclose( cfPtr ); } return 0; } </code></pre> <hr> <pre><code>/*To read the File*/ #include &lt;stdio.h&gt; struct clientsData{ int account; char lastname[ 30 ], name[ 30 ]; double balance; }; int main(void) { FILE *cfPtr; struct clientsData client = { 0, "", "", 0.0 }; if( ( cfPtr = fopen( "clients.dat", "rb" ) ) == NULL ) { printf( "File couldn't be opened. " ); } else{ printf( "%-6s%-16s%-11s%10s\n", "Acct", "Lastname", "Firstname", "Balance" ); while( !feof( cfPtr ) ){ fread( &amp;client, sizeof( struct clientsData ), 1, cfPtr ); if( client.account != 0 ){ printf( "%-6d%-16s%-11s%10.2f\n", &amp;client.account, client.lastname, client.name, &amp;client.balance ); } } fclose( cfPtr ); } return 0; } </code></pre>
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    1. USAlberto Bonsanto
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    1. CO*"And i thought well, maybe the double representation doesn't match with the reading program (notepad)."* This is correct, just to clear that up. The double is being stored in 64-bit IEEE Floating Point format, which is not (easily) readable by humans. (And certainly not once interpreted as text.)
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      1. UScdhowie
    2. CO@DanielFischer That's not the problem; he's writing the entire struct value as a distinct record to disk, and reading it back the same way. The data file format will be dependent on the compiler used, but other than that there are no problems with this approach.
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      1. UScdhowie
    3. CO@cdhowie Yeah, stopped reading at "notepad" ;)
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      1. USDaniel Fischer
 

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