Common Mistakes

Recurring problems when working with BGL property maps, with minimal reproduction and fixes.

Category mismatch

make_function_property_map produces a read-only map. Passing it where an algorithm expects ReadWrite fails to compile. The color_map and distance_map parameters are written to by most algorithms.

Broken

auto color = make_function_property_map<Vertex>([](Vertex) {
    return default_color_type::white_color;
});
breadth_first_search(g, s, visitor(default_bfs_visitor()),
    color_map(color));
// Compile error: no matching function for call to 'put'

The algorithm calls put(color, v, gray) during traversal, but make_function_property_map does not support put.

Fix: use a vector instead

std::vector<default_color_type> colors(num_vertices(g));
auto color = make_iterator_property_map(colors.begin(), get(vertex_index, g));

Container too small

A vector sized to N when the graph has N + 1 vertices causes silent out-of-bounds writes. Results are wrong or the program crashes intermittently.

Broken

std::vector<int> dist(10);  // hope the graph has <= 10 vertices
auto dist_map = make_iterator_property_map(dist.begin(), get(vertex_index, g));

Fix: always size from the graph

std::vector<int> dist(num_vertices(g));
auto dist_map = make_iterator_property_map(dist.begin(), get(vertex_index, g));

Dangling storage

A vector allocated inside a function is destroyed when the function returns. Any property map that wraps it becomes a dangling reference.

Broken

auto make_map(const Graph& g) {
    std::vector<double> v(num_vertices(g), 0.0);
    return make_iterator_property_map(v.begin(), get(vertex_index, g));
    // v is destroyed here; the returned map points to freed memory
}

Fix: allocate in the caller scope

std::vector<double> v(num_vertices(g), 0.0);
auto pm = make_iterator_property_map(v.begin(), get(vertex_index, g));
// v and pm have the same lifetime

Alternatively, use vector_property_map which owns its storage internally.

Missing include

vector_property_map lives in its own header. Omitting the include produces long template errors that do not mention the missing header.

Broken

#include <boost/property_map/property_map.hpp>  // not enough
vector_property_map<double> pm(num_vertices(g), get(vertex_index, g));
// error: 'vector_property_map' was not declared in this scope

Fix

#include <boost/property_map/vector_property_map.hpp>

Const graph, wrong property map type

When a function receives const Graph&, you need const_type instead of type. Using the wrong one produces long template errors.

Broken

void analyze(const Graph& g) {
    property_map<Graph, edge_weight_t>::type w = get(edge_weight, g);
    // error: conversion from const_type to type
}

Fix: use const_type for const graphs

void analyze(const Graph& g) {
    property_map<Graph, edge_weight_t>::const_type w = get(edge_weight, g);
}

Or simply use auto.

No automatic edge_index

Unlike vertex_index_t which is provided automatically when VertexList=vecS, there is no automatic edge_index. You must declare it explicitly and assign values manually.

Broken

auto eidx = get(edge_index, g);  // compile error if edge_index not declared

Fix: declare edge_index in the graph type

using Graph = adjacency_list<vecS, vecS, directedS,
    no_property,
    property<edge_index_t, std::size_t>>;
// Assign indices when adding edges:
add_edge(0, 1, 0, g);
add_edge(1, 2, 1, g);

No vertex_index with listS

With VertexList = listS, there is no built-in vertex_index property. This breaks not just get(vertex_index, g) but also any algorithm that internally creates default property maps (color maps, distance maps, etc.) using vertex_index. BFS, DFS, Dijkstra, copy_graph, topological_sort, and most other algorithms are affected.

Broken

using Graph = adjacency_list<vecS, listS, directedS>;
Graph g;
// ...
auto idx = get(vertex_index, g);  // compile error

Fix: supply your own index

using Vertex = graph_traits<Graph>::vertex_descriptor;
std::map<Vertex, int> index_map;
int i = 0;
for (auto [vi, vi_end] = vertices(g); vi != vi_end; ++vi) {
    index_map[*vi] = i++;
}
auto idx = make_assoc_property_map(index_map);

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