Graph I/O
BGL supports reading and writing graphs in three formats.
| Format | Best for | Properties | Linking |
|---|---|---|---|
GraphViz (DOT) |
Visualization, general exchange |
Arbitrary vertex, edge, and graph attributes |
Requires |
GraphML (XML) |
Interoperability with other graph tools |
Typed attributes with XML schema |
Requires |
DIMACS |
Max-flow / min-cut benchmarks |
Edge capacity only |
Header-only |
GraphViz and GraphML parsers require linking against libboost_graph because
they contain non-template code: the DOT parser uses a grammar that cannot be
instantiated in a header, and the GraphML reader depends on an XML parser.
DIMACS is a trivial line-oriented format and is fully header-only.
| Property map value types must be default-constructible. Unspecified attributes receive default-constructed values during reading. |
The graph’s directionality must match the file. Reading a digraph
(DOT) or directed edges (GraphML) into an undirected graph type throws
directed_graph_error. The reverse throws undirected_graph_error.
|
dynamic_properties
File formats store attributes by name: a vertex might have a "name" string
and an edge might have a "weight" double. BGL property maps are type-safe
but have no name. get(vertex_name, g) is a compile-time tag, not a string.
dynamic_properties bridges this gap. It is a runtime registry that binds
string names (as they appear in the file) to typed BGL property maps. The I/O
functions use it to know which file attribute maps to which property map, and
what type to read or write.
dynamic_properties dp;
// Bind the string "name" to the vertex_name property map
dp.property("name", get(vertex_name, g));
// Bind the string "weight" to the edge_weight property map
dp.property("weight", get(edge_weight, g));The same dynamic_properties object is then passed to both read and write
functions. When reading, the parser looks up each attribute name in the
registry and calls put() on the corresponding map. When writing, each
registered map is queried with get() for every vertex or edge.
By default, dynamic_properties throws property_not_found if the
file contains an attribute that was not registered. To silently skip unknown
attributes, pass ignore_other_properties to the constructor:
|
dynamic_properties dp(ignore_other_properties);
dp.property("weight", get(edge_weight, g));
// All other attributes in the file are silently ignored