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Kazade

STL or Boost equivalent of sscanf?

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Hi, Im trying to pass a half-life .map file. Planes are defined in the file like this:
( 432 0 96 ) ( 432 128 96 ) ( 560 0 96 ) FIFTIES_WALL14Y [ 1.00000 0.00000 0.00000 -432.00000 ]  [ 0.00000 -1.00000 0.00000 0.00000 ]  0  1.00000 1.00000

Now, normally I'd use sscanf to parse this string, but I'm thinking there must be a C++ way of doing this with streams. But I cant find any information on how to do this without reverting back to sscanf. Boost has a format library, but that only works the other way (ie putting arguments into a string not taking them out). Anyone know the best way of doing this? Thanks, Luke.

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If you're able to properly parse it with sscanf then ordinary streams are probably adequate. For more advanced needs you might try Boost.Tokenizer or maybe even Boost.Spirit, though that may be overkill.

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Something like this:


struct triple {
int values[3];
};

struct quad {
float values[4];
}

template<typename T>
void expect(istream& is, const T& expected) {
T got;
is >> got;
if (got != expected) { is.setstate(ios::fail_bit); }
}

// For safety... when checking a char*, use the string version,
// so that 'got' will actually be a valid buffer for reading.
void expect(istream& is, const char*& expected) {
expect(is, string(expected));
}

void rewind_if_failed(istream& is, streampos pos) {
if (!is) {
iostate tmp = is.rdstate();
is.clear();
is.seekg(pos);
is.setstate(tmp);
}
}

// These are implemented like the primitive types, in that if the thing can't
// be read, then nothing should appear consumed from the stream, and the
// stream will be in a failed state. That allows you to handle a situation
// where two possible kinds of things are valid at a given point in the
// stream: if one read-attempt fails, reset and try to read the other type.

istream& operator>>(istream& is, triple& t) {
streampos current = is.tellg();
expect(is, "(");
is >> t.values[0] >> t.values[1] >> t.values[2];
expect(is, ")");
rewind_if_failed(is);
}

istream& operator>>(istream& is, quad& q) {
streampos current = is.tellg();
expect(is, "[");
is >> q.values[0] >> q.values[1] >> q.values[2] >> q.values[3];
expect(is, "]");
rewind_if_failed(is);
}

// now we use a stringstream like this:
string line;
getline(is, line); // load a line of the file into our string.
stringstream ss(line);
triple a, b, c;
string texture_name;
quad x, y;
float f1, f2, f3;
line >> a >> b >> c >> texture_name >> x >> y >> f1 >> f2 >> f3;

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