'gvLayout' crashing

Dev
1

Any idea why this simple example would be crashing?

void testGraphviz(void)
{
	GVC_t *gvc = gvContext();
	Agraph_t *graf = agopen("MyGraf", Agdirected, nullptr);
	Agsym_t *attr = agattr(graf, AGNODE, "label", "Default label");
	Agnode_t *n1 = agnode(graf, "N1", 1);
	Agnode_t *n2 = agnode(graf, "N2", 1);
	Agedge_t *e = agedge(graf, n1, n2, "", TRUE);	
	gvLayout(gvc, graf, "dot");  // crashes with "Exception at..." error
}

Note that Graphviz is actually working correctly in my app, but the code is scattered and would be too complicated to post here. The steps above are exactly the same as what I’m invoking when it works, but I can’t determine what the difference is. All pointers return not null.

ND_label(n1) also returns an invalid address.

gvLayoutCrash
gvLayoutCrash502×141 5.08 KB

2

I’ve made some progress. The following program builds & runs fine in Visual Studio:

// TestGraphviz.cpp
//

#include "pch.h"
#include <iostream>
#define GVDLL		// https://stackoverflow.com/questions/77733103/cant-use-graphviz-as-a-library-in-c
#include <F:\Program Files\Graphviz\include\graphviz\gvc.h>

int main()
{	char MyGraf[] = "MyGraf", label[] = "label", style[] = "style", fillcolor[] = "fillcolor", color[] = "color", 
		fontcolor[] = "fontcolor", shape[] = "shape", fontname[] = "fontname", fontsize[] = "fontsize", N1[] = "N1", N2[] = "N2",
		empty[] = "";
    std::cout << "Hello World!\n"; 
	GVC_t *gvc = gvContext();
	if(gvc == nullptr)
		return 0;
	std::cout << "\ngvc " << gvc << "\n";
	Agraph_t *graf = agopen(MyGraf, Agdirected, nullptr);
	if(graf == nullptr)
		return 0;
	std::cout << "graf " << graf << "\n";

	Agsym_t *attr = agattr(graf, AGNODE, label, "Default label");
	agattr(graf, AGNODE, style, "filled");
	agattr(graf, AGNODE, fillcolor, "white");
	agattr(graf, AGNODE, color, "black");
	agattr(graf, AGNODE, fontcolor, "black");
	agattr(graf, AGNODE, shape, "box");
	agattr(graf, AGNODE, fontname, "Arial");
	agattr(graf, AGNODE, fontsize, "12");
	
	Agnode_t *n1 = agnode(graf, N1, 1);
	if(n1 == nullptr)
		return 0;
	int r1 = agset(n1, label, "Node 1");
	
	Agnode_t *n2 = agnode(graf, N2, 1);
	if(n2 == nullptr)
		return 0;
	int r2 = agset(n2, label, "Node 2");

	Agedge_t *e = agedge(graf, n1, n2, empty, true);	
	if(e == nullptr)
		return 0;
	
	gvLayout(gvc, graf, "dot");
	std::cout << "n1 " << n1 << ND_label(n1)->text << " r1 " << r1 << "\n";
	std::cout << "n2 " << n2 << ND_label(n2)->text << " r2 " << r2 << "\n";
	
	std::cout << "\n" << ND_pos(n1) << ND_label(n1)->text << "\n";
	return 0;
}

You need to link cgraph.lib and gvc.lib

However, the same code crashes at gvLayout when built with Qt 5.13. I link cgraph.lib and gvc.lib. I’ve tried with and without cgraph++.lib, gvc++.lib and cdt.lib.

I’d attach the source and project files if they let me.

Any Qt’ers out there? Can you reproduce the problem?