That solved my problem. Thank you very much. BTW - if you used write_graphviz perhabs you could use gvRenderData or gvRender too. I'm trying to display rendered graph image but without storing it in temoprary file. So i found gvRenderData from graphviz library most suitable to do that. But when i call this function it simply seems not to be working. when I type something like that: write_graphviz(my_stringstream, graf->Get_g()); g = agmemread(const_cast<char*>(my_stringstream.str().c_str())); gvLayout(gvc, g, "dot"); gvRenderFilename (gvc, g, "png","out.png"); I get valid png file and everything is OK. But if i do this: write_graphviz(my_stringstream, graf->Get_g()); g = agmemread(const_cast<char*>(my_stringstream.str().c_str())); gvLayout(gvc, g, "dot"); char* data; int result = gvRenderData(gvc, g, "png", &data); // result = 0 so that should be OK std::ofstream my_fstream("picture.png" , std::fstream::binary); while(*data!=EOF) my_fstream.put(*(data++)); stru.close(); than an output file - picture.png is not valid and have smaller size than out.png in first example. I tried to change the following line: while(*data!=EOF) to: while(*data!='\0') but it still is not correct. Maybe you've got some example of using vgRenderData - i would be gratefull. If not - that's not a big deal - you've already helped me so much. Cheers, Michał Nowotka