# fn()topologicalSortPerforms a topological sort on a directed acyclic graph (DAG).

Defined in ```void topologicalSort(g, topSort); ```

## Parameters

 `g` A directed acyclic graph. Types: Directed Graph A topological ordering of the vertices. Types: String.

## Detailed Description

A topological sort is a linear ordering of all its vertices such that if the graph contains an edge (u,v) then u appears before v in the ordering.

### Example

```#include <iostream>
#include <seqan/graph_algorithms.h>

using namespace seqan;

int main()
{
typedef Graph<Directed<> > TGraph;
typedef VertexDescriptor<TGraph>::Type TVertexDescriptor;
typedef EdgeDescriptor<TGraph>::Type TEdgeDescriptor;
typedef Size<TGraph>::Type TSize;

// Create graph with 9 directed edges (0,3), (0,1), ...
TSize numEdges = 9;
TVertexDescriptor edges[] = {0,3, 0,1, 1,2, 3,2, 5,7, 5,6, 6,7, 6,3, 8,7};
TGraph g;
// Print graph.
std::cout << g << "\n";

// Create external property map with vertex labels.
String<std::string> nameMap;
std::string names[] = {"shirt", "tie", "jacket", "belt", "watch", "undershorts", "pants", "shoes", "socks"};
assignVertexMap(g, nameMap, names);

// Get vertex descriptor in topological sort order.
String<TVertexDescriptor> order;
topologicalSort(g, order);

// Write the result to stdout.
std::cout << "Topological sort: \n";
typedef Iterator<String<TVertexDescriptor> >::Type TStringIterator;
TStringIterator it = begin(order);
TStringIterator itEnd = end(order);
while (it != itEnd)
{
std::cout << getProperty(nameMap, getValue(it)) << ",";
goNext(it);
}
std::cout << "\n";

return 0;
}
```
```Adjacency list:
0 -> 1,3,
1 -> 2,
2 ->
3 -> 2,
4 ->
5 -> 6,7,
6 -> 3,7,
7 ->
8 -> 7,
Edge list:
Source: 0,Target: 1 (Id: 1)
Source: 0,Target: 3 (Id: 0)
Source: 1,Target: 2 (Id: 2)
Source: 3,Target: 2 (Id: 3)
Source: 5,Target: 6 (Id: 5)
Source: 5,Target: 7 (Id: 4)
Source: 6,Target: 3 (Id: 7)
Source: 6,Target: 7 (Id: 6)
Source: 8,Target: 7 (Id: 8)

Topological sort:
socks,undershorts,pants,shoes,watch,shirt,belt,tie,jacket,
```