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57 lines
2.4 KiB
Plaintext
57 lines
2.4 KiB
Plaintext
Interfacing with C
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Interfacing ETL containers with contiguous storage to a C API is fairly easy to do.
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____________________________________________________________________________________________________
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This is a C function that copies count characters , starting from 'a', to a buffer pointed to by start.
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size_t CFunctionCopyToBuffer(char* start, size_t count)
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{
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size_t i = 0;
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while (i < count)
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{
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*p++ = 'a' + i;
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++i;
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}
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return i;
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}
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____________________________________________________________________________________________________
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Array
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The ETL array is simply a C array wrapped in a C++ interface.
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size_t length;
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etl::array<char, 26> buffer;
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length = CFunctionCopyToBuffer(buffer.data(), buffer.max_size() / 2);
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Array contains [ a, b, c, d, e, f, g, h, i, j, k, l, m ]
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____________________________________________________________________________________________________
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Vector
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To use a vector with C, you must make room for the expected new data, and then adjust to the new size after copying.
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etl::vector<char, 26> buffer;
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buffer.uninitialized_resize(buffer.max_size()); // Make the vector as big as it can be.
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size_t newLength = CFunctionCopyToBuffer(buffer.data(), buffer.max_size() / 2);
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buffer.resize(newLength); // Now adjust it back to the actual new size.
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Vector contains [ a, b, c, d, e, f, g, h, i, j, k, l, m ]
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____________________________________________________________________________________________________
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String
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Strings are terminated with null characters. We can use this to easily adjust the length after copying.
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etl::string<26> buffer;
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buffer.initialize_free_space(); // Ensure that the string's free space are terminators characters.
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CFunctionCopyToBuffer(buffer.data(), buffer.max_size() / 2);
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buffer.trim_to_terminator(); // Trim the string length at the first null terminator.
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String contains "abcdefghijklm"
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// Lets add some more characters. Start at data_end() so we append to what's already there.
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// We'll use the alternative method to adjust the string length.
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// We could still use trim_to_terminator() if we wanted to.
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size_t oldSize = buffer.size(); // Remember the current size.
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buffer.uninitialized_resize(buffer.max_size()); // Make the string as big as it can be.
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size_t appendedSize = CFunctionCopyToBuffer(buffer.data_end(), buffer.max_size() / 2);
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buffer.uninitialized_resize(oldSize + appendedSize); // Now adjust it back to the actual new size.
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String contains "abcdefghijklmabcdefghijklm"
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