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POC++ Parsing a line out of a large file
 

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  1. POC++ Parsing a line out of a large file
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    <p>I have read an entire file into a string from a memory mapped file Win API </p> <pre><code>CreateFile( "WarandPeace.txt", GENERIC_READ, FILE_SHARE_READ, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0 ) </code></pre> <p>etc...</p> <p>Each line is terminated with a CRLF. I need to find something on a line like "Spam" in the line "I love Spam and Eggs" (and return the entire line (without the CRLF) in a string (or a pointer to the location in the string) The original string cannot be altered.</p> <p><strong>EDITED:</strong></p> <p>Something like this:</p> <pre><code>string ParseStr( string sIn, string sDelim, int nField ) { int match, LenStr, LenDelim, ePos, sPos(0), count(0); string sRet; LenDelim = sDelim.length(); LenStr = sIn.length(); if( LenStr &lt; 1 || LenDelim &lt; 1 ) return ""; // Empty String if( nField &lt; 1 ) return ""; //=========== cout &lt;&lt; "LenDelim=" &lt;&lt; LenDelim &lt;&lt; ", sIn.length=" &lt;&lt; sIn.length() &lt;&lt; endl; for( ePos=0; ePos &lt; LenStr; ePos++ ) // iterate through the string { // cout &lt;&lt; "sPos=" &lt;&lt; sPos &lt;&lt; ", LenStr=" &lt;&lt; LenStr &lt;&lt; ", ePos=" &lt;&lt; ePos &lt;&lt; ", sIn[ePos]=" &lt;&lt; sIn[ePos] &lt;&lt; endl; match = 1; // default = match found for( int k=0; k &lt; LenDelim; k++ ) // Byte value { if( ePos+k &gt; LenStr ) // end of the string break; else if( sIn[ePos+k] != sDelim[k] ){ // match failed match = 0; break; } } //=========== if( match || (ePos == LenStr-1) ) // process line { if( !match ) ePos = LenStr + LenDelim; // (ePos == LenStr-1) count++; // cout &lt;&lt; "sPos=" &lt;&lt; sPos &lt;&lt; ", ePos=" &lt;&lt; ePos &lt;&lt; " &gt;" &lt;&lt; sIn.substr(sPos, ePos-sPos) &lt;&lt; endl; if( count == nField ){ sRet = sIn.substr(sPos, ePos-sPos); break; } ePos = ePos+LenDelim-1; // jump over Delim sPos = ePos+1; // Begin after Delim } // cout &lt;&lt; "Final ePos=" &lt;&lt; ePos &lt;&lt; ", count=" &lt;&lt; count &lt;&lt; ", LenStr=" &lt;&lt; LenStr &lt;&lt; endl; }// next return sRet; } </code></pre> <p>If you like it, vote it up. If not, let's see what you got.</p>
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    1. USMike Trader
    1. USMike Trader
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      1. POC++ Parsing a line out of a large file
      1. USMike Trader
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    1. COCreateFile() does not memory map a file. It only opens it. Do you actually call CreateFileMapping() and MapViewOfFile() after that?
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      1. POC++ Parsing a line out of a large file
      1. USÉric Malenfant
    2. COAnother confusing aspect: If you actually memory map the file, why copy it in a string afterwards?
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      1. USÉric Malenfant
    3. COIt's an exercise in parsing. But there are times when you need to parse lines out of a memory mapped file, or even the response from an HTTP request etc.
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      1. USMike Trader
 

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