106 lines
2.5 KiB
C++
106 lines
2.5 KiB
C++
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Read Text Files
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void main()
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{
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char pcMyLines[10000];
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ReadLines("C:\\MyTestFile.txt", 10, 5, pcMyLines, 12345);
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}
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// This function reads n lines from a file
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// Returns the amount of bytes read
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int ReadLines(const char *pcFile, const int iStartLine, const int iTotLines, char *pcBuffer, const int iBufLen)
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{
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FILE *fSrc;
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int iLines = 0, j, iPos, iByteCount = 0;
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// Try to open the file
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if(fSrc = fopen(pcFile, "r"))
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{
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// Try to locate the starting line
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if(iPos = GetLinePos(fSrc, iStartLine))
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{
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// Set the starting position
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if(!fseek(fSrc, iPos, SEEK_SET))
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{
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// Read the lines
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for(iLines=0;iLines<iTotLines;iLines++)
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{
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// Read the line
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if((j = ReadLine(fSrc, iPos, pcBuffer, iBufLen - iByteCount)) == -1) break;
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iByteCount += j;
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}
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}
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}
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// Close the file
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fclose(fSrc);
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}
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// Return the amount of bytes in the buffer, or -1 for failure
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return iLines == iTotLines ? iByteCount : -1;
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}
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// This function reads a single line from a file
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int ReadLine(FILE *fSrc, const int iStartPos, char *pcBuffer, const int iBufLen)
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{
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int iCount = 0;
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// Set the starting position
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if(!fseek(fSrc, iStartPos, SEEK_SET))
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{
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// Keep reading characters while we can
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while(!feof(fSrc) && (iCount < iBufLen))
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{
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// Read the character
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pcBuffer[iCount] = (char)fgetc(fSrc);
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if(pcBuffer[iCount++] == '\n') break;
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}
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}
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else iCount = -1;
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return iCount;
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}
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// This function locates a line in a file
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// Returns the position of the line in the file
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int GetLinePos(FILE *fSrc, const int iLine, const int iStartPos /* 0 */)
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{
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char pcBuffer[4096];
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int i, iPos = 0, iLines = 0, iBytes;
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// Set the start position
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if(!fseek(fSrc, iStartPos, SEEK_SET))
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{
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// Read the (next) block of data
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while(iBytes = fread(pcBuffer, sizeof(char), 4096, fSrc))
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{
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// Go through the block
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for(i=0;i<iBytes;i++)
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{
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// Do we have a new line?
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if(pcBuffer[i] == '\n')
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{
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// Update the line count
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iLines++;
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// Have we reached the desired line?
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if(iLines == iLine)
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{
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// Store the position
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iPos += i;
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break;
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}
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}
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}
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// Update the position
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iPos += iBytes;
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}
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}
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// Return the position of the line in the file, or -1 for failure
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return iLines == iLine ? iPos : -1;
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}
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