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#include <Functions/FunctionFactory.h>
#include <Functions/FunctionStringToString.h>
#include <Functions/StringHelpers.h>
#include <base/find_symbols.h>
namespace DB
{
struct FirstLine
{
static size_t getReserveLengthForElement() { return 16; }
static void execute(Pos data, size_t size, Pos & res_data, size_t & res_size)
{
res_data = data;
const Pos end = data + size;
const Pos pos = find_first_symbols<'\r', '\n'>(data, end);
res_size = pos - data;
}
};
struct NameFirstLine
{
static constexpr auto name = "firstLine";
};
using FunctionFirstLine = FunctionStringToString<ExtractSubstringImpl<FirstLine>, NameFirstLine>;
REGISTER_FUNCTION(FirstLine)
{
factory.registerFunction<FunctionFirstLine>(FunctionDocumentation{
.description = "Returns first line of a multi-line string.",
.syntax = "firstLine(string)",
.arguments = {{.name = "string", .description = "The string to process."}},
.returned_value = {"The first line of the string or the whole string if there is no line separators."},
.examples = {
{.name = "Return first line", .query = "firstLine('Hello\\nWorld')", .result = "'Hello'"},
{.name = "Return whole string", .query = "firstLine('Hello World')", .result = "'Hello World'"},
}});
}
}
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