我一直在收到消息 Graph.h：在函数'bool has_cycle（G＆amp;）'中： Graph.h：392：5：错误：在'{'标记之前预期';' 我已经检查了所有支架，它们是平衡的，我无法弄清楚为什么我
错误发生在has_cycle函数中。我想知道它是否与模板函数参数
有关#ifndef Graph_h
#define Graph_h
// --------
// includes
// --------
#include <cassert> // assert
#include <cstddef> // size_t
#include <utility> // make_pair, pair
#include <deque> // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered set
#include <iterator>
#include <algorithm>
#include "boost/graph/exception.hpp"// not_a_dag exception
// -----
// Graph
// -----
class Graph
{
public:
//EdgeDescriptor Class
class EdgeDescriptor
{
public:
std::size_t _source; /*!< source vertex_descriptor */
std::size_t _target; /*!< target vertex_descriptor */
/**
* default constructor
*/
EdgeDescriptor()
{}
/**
* constructor
* @param s the sourse vertex_descriptor
* @param t the target vertex_descriptor
*/
EdgeDescriptor(std::size_t s, std::size_t t)
{
_source = s;
_target = t;
}
/**
* == operator for EdgeDescriptor
* @param lhs a EdgeDescriptor
* @param rhs a EdgeDescriptor
* @return a bool that indicates whether the EdgeDescriptors are equal
*/
friend bool operator == (const EdgeDescriptor& lhs, const EdgeDescriptor& rhs)
{
return (lhs._source == rhs._source) && (lhs._target == rhs._target);
}
};
// --------
// typedefs
// --------
typedef std::size_t vertex_descriptor;
typedef EdgeDescriptor edge_descriptor;
typedef std::deque<vertex_descriptor>::iterator vertex_iterator;
typedef std::unordered_set<edge_descriptor>::iterator edge_iterator;
typedef std::deque<vertex_descriptor>::iterator adjacency_iterator;
typedef std::size_t vertices_size_type;
typedef std::size_t edges_size_type;
public:
// --------
// add_edge
// --------
/**
* possibly add an edge_descriptor between two given vertex_descriptor to the graph
* @param v1 a vertex_descriptor
* @param v2 a vertex_descriptor
* @return a pair where first of the pair is the edge_descriptor added and second of the pair indicates whether the EdgeDescriptor has been successfully added
*/
friend std::pair<edge_descriptor, bool> add_edge (vertex_descriptor v1, vertex_descriptor v2, Graph& g)
{
edge_descriptor e(v1, v2);
//check if the edge_descriptor exists in the graph
if(g._edges.find(e) == g._edges.end())
{
/* If the VertexList selector is vecS, and if either vertex descriptor u or v (which are integers) has a value greater than the current number of vertices in the graph,
the graph is enlarged so that the number of vertices is std::max(u,v) + 1. */
if((v1 >= g._vertices.size()) || (v2 >= g._vertices.size()))
{
std::size_t new_size = std::max(v1, v2) + 1;
g._vertices.resize(new_size);
}
g._targets[v1].push_back(v2); //add v1's adjacent vertex_descriptor (which is v2)
g._edges.insert(e); //add edge_descriptor
return std::make_pair(e, true);
}
else
{
return std::make_pair(e, false);
}
}
// ----------
// add_vertex
// ----------
/**
* add a vertex_descriptor to the graph
* @param g the graph where vertex_descriptor is added
* @return the vertex_descriptor added
*/
friend vertex_descriptor add_vertex (Graph& g)
{
g._vertices.push_back((g._vertices.size()) + 1);
return g._vertices.back();
}
// -----------------
// adjacent_vertices
// -----------------
/**
* adjacent_vertices function
* @param v a vertex_descriptor
* @param g the graph where the vertex_descriptor is
* @return a pair of adjacency_iterators, where the first iterator can travel to the second one the eventually visit all the adjacent vertices of the vertex_descriptor
*/
friend std::pair<adjacency_iterator, adjacency_iterator> adjacent_vertices (vertex_descriptor v, Graph& g)
{
return std::make_pair(((g._targets.find(v))->second).begin(), ((g._targets.find(v))->second).end());
}
// ----
// edge
// ----
/**
* edge function
* @param v1 a vertex_descriptor
* @param v2 a vertex_descriptor
* @param g the graph where the vertex_descriptor is
* @return a pair, where first is the edge_descriptor between the vertices, second is a bool indicates whether the edge_descriptor exists in the graph
*/
friend std::pair<edge_descriptor, bool> edge (vertex_descriptor v1, vertex_descriptor v2, const Graph& g)
{
edge_descriptor e(v1, v2);
if(g._edges.find(e) == g._edges.end())
{
return std::make_pair(e, true);
}
else
{
return std::make_pair(e, false);
}
}
// -----
// edges
// -----
/**
* edges function
* @param g a Graph
* @return a pair of edge_iterator in which the first can travel to the second one the eventually visits all the edges in the given graph
*/
friend std::pair<edge_iterator, edge_iterator> edges (Graph& g)
{
return std::make_pair(g._edges.begin(), g._edges.end());
}
// ---------
// num_edge
// ---------
/**
* num_edge function
* @param g a Graph
* @return the number of edges in the given graph
*/
friend edges_size_type num_edge (const Graph& g)
{
return g._edges.size();
}
// ------------
// num_vertices
// ------------
/**
* num_vertices function
* @param g a Graph
* @return the number of vertices in the given graph
*/
friend vertices_size_type num_vertices (const Graph& g)
{
return g._vertices.size();
}
// ------
// source
// ------
/**
* source function
* @param r an edge_descriptor
* @param g a Graph
* @return the source vertex_descriptor of a given edge_descriptor in the given graph
*/
friend vertex_descriptor source (edge_descriptor e, const Graph& g)
{
return (g._edges.find(e))->_source;
}
// ------
// target
// ------
/**
* target function
* @param e an edge_descriptor
* @param g a Graph
* @return the target vertex_descriptor of a given edge_descriptor in the given graph
*/
friend vertex_descriptor target (edge_descriptor e, const Graph& g)
{
return (g._edges.find(e))->_target;
}
// ------
// vertex
// ------
/**
* vertex function
* @param nth integral value represents the n term index of the vertex
* @param g a Graph
* @return the nth vertex_descriptor of the graph
*/
friend vertex_descriptor vertex (vertices_size_type nth, const Graph& g)
{
return g._vertices[nth];
}
// --------
// vertices
// --------
/**
* vertices function
* @param g a Graph
* @return a pair of vertex_iterator in which the first can travel to the second one the eventually visits all the vertices in the given graph
*/
friend std::pair<vertex_iterator, vertex_iterator> vertices (Graph& g)
{
return std::make_pair(g._vertices.begin(), g._vertices.end());
}
private:
// ----
// data
// ----
std::deque<vertex_descriptor> _vertices; /*!< container of the vertex_descriptors */
std::unordered_set<edge_descriptor> _edges; /*!< container of the edge_descriptors */
std::unordered_map<vertex_descriptor, std::deque<vertex_descriptor> > _targets; /*!< keep track of the adjacent vertices (vertex_descriptor that vertex_descriptors points to). Key is the vertex_descriptor that owns the adjacent vertex_descriptors*/
// -----
// valid
// -----
/**
* valid function
*/
bool valid () const
{
return _vertices.size() == 0 && _edges.size() == 0 && _targets.size() == 0;
}
public:
// ------------
// constructors
// ------------
/**
* default constructor
*/
Graph () : _vertices(), _edges(), _targets()
{
assert(valid());
}
// Default copy, destructor, and copy assignment
// Graph (const Graph<T>&);
// ~Graph ();
// Graph& operator = (const Graph&);
};
//helper function for has_cycle
template <typename G>
bool has_grey_neighbour (const G& g, typename G::vertex_descriptor v, std::vector<int>& colors)
{
return std::any_of(adjacent_vertices(v, g).first, adjacent_vertices(v, g).second, [&colors](typename G::vertex_descriptor v)
{
return colors[v] == 1;
});
}
//helper function for DFS (return -1 if no)
template <typename G>
int get_white_vertex (const G& g, std::vector<int>& colors)
{
int result = -1;
int count = 0;
while(count < colors.size() && result == -1)
{
if(colors[count] == 0)
{
result = count;
}
++count;
}
return result;
}
//helper function for DFS (return -1 if no white neighbour)
template <typename G>
int get_white_neighbour (const G& g, typename G::vertex_descriptor v, std::vector<int>& colors)
{
typename G::adjacency_iterator match;
match = std::find_if(adjacent_vertices(v, g).first, adjacent_vertices(v, g).second, [&colors](typename G::vertex_descriptor v)
{
return colors[v] == 0;
});
if(match == adjacent_vertices(v, g).second)
{
return -1;
}
else
{
return (int)(*match);
}
}
// ---------
// has_cycle
// ---------
/**
* depth-first traversal
* three colors
* @param g a Graph
* @return bool indicates whether the graph is cyclic
*/
template <typename G>
bool has_cycle (const G& g)
{
if(num_vertices(g) == 0)
{
return false;
}
std::vector<int> colors(num_vertices(g), 0); //keep track of the different colors of vertices (0 while, 1 grey, 2 black)
std::deque<typename G::vertex_descriptor> s; //use as a stack
typename G::vertex_descriptor current_vertex;
int current_vertex_index;
int next_vertex_index;
bool stack_empty;
whlie(get_white_vertex(g, colors) != -1)
{
current_vertex_index = get_white_vertex(g, colors);
current_vertex = vertex(current_vertex_index, g);
colors[current_vertex_index] = 1;
do
{
if(has_grey_neighbour(g, current_vertex, colors))
{
return true;
}
if((next_vertex_index = get_white_neighbour(g, current_vertex, colors)) != -1)
{
colors[next_vertex_index] = 1;
s.push_back(current_vertex);
current_vertex = vertex(next_vertex_index, g);
current_vertex_index = (int)current_vertex;
}
else
{
colors[current_vertex_index] = 2;
if(!(stack_empty = s.empty()))
{
current_vertex = s.back();
current_vertex_index = (int)current_vertex;
s.pop_back();
}
}
}while(!stack_empty);
}
return false;
}
// ----------------
// topological_sort
// ----------------
/**
* depth-first traversal
* two colors
* performs a topological sort on a graph and stream the outoput to an output iterator
* @param g a Graph
* @param x an output iteration
* @throws Boost's not_a_dag exception if has_cycle()
*/
template <typename G, typename OI>
void topological_sort (const G& g, OI x)
{
if(has_cycle(g))
{
throw boost::not_a_dag();
}
else
{
std::vector<int> colors(num_vertices(g), 0); //keep track of the different colors of vertices (0 while, 1 grey, 2 black)
std::deque<typename G::vertex_descriptor> s; //use as a stack
int current_vertex_index;
int next_vertex_index;
bool stack_empty;
typename G::vertex_descriptor current_vertex;
std::deque<typename G::vertex_descriptor> result;
whlie((current_vertex_index = get_white_vertex(g, colors)) != -1)
{
current_vertex = vertex(current_vertex_index, g);
colors[current_vertex_index] = 1;
do
{
if((next_vertex_index = get_white_neighbour(g, current_vertex, colors)) != -1)
{
colors[next_vertex_index] = 1;
s.push_back(current_vertex);
current_vertex = vertex(next_vertex_index, g);
current_vertex_index = (int)current_vertex;
}
else
{
colors[current_vertex_index] = 2;
if(!(stack_empty = s.empty()))
{
current_vertex = s.back();
current_vertex_index = (int)current_vertex;
s.pop_back();
}
}
}while(!stack_empty);
}
while(!result.empty())
{
*x = result.back();
result.pop_back();
++x;
}
}
}
#endif // Graph_h
答案 0 :(得分：5)
While拼写错误：
whlie((current_vertex_index = get_white_vertex(g, colors)) != -1)