Segmentation Fault using Tinyxml

Question

I'm trying to read an Xml file recursively using Tinyxml, but when I try to acces the data I get a "Segmentation Fault". here is the code :

int id=0, categoria=0;
const char* nombre;
do{  
    ingrediente = ingrediente->NextSiblingElement("Ingrediente");   
    contador++;  
    if(ingrediente->Attribute("id")!=NULL)
        id = atoi( ingrediente->Attribute("id") );  
    if(ingrediente->Attribute("categoria")!=NULL)
        categoria = atoi ( ingrediente->Attribute("categoria") );  
    if(ingrediente!=NULL)
        nombre = ( ( ingrediente->FirstChild() )->ToText() )->Value();  
}while(ingrediente);

For some reason, the three "if" lines throws me the Segmentation Fault but I've not idea about where is the problem.

Thanks in advance.

It looks like you check if ingrediente!=NULL on the third if but not on the first two. If ingrediente really was null then those first two if's would throw a segmentation fault. You should open this up with a debugger to find out exactly what is NULL. — Pace, Aug 14 '10 at 00:05
You'd get a precise answer if you'd post a complete code, and don't forget to use the "code" tag so it gets formatted properly. I suggest you edit. — Poni, Aug 14 '10 at 00:18
And you'll do even better if you'll post a "mini-version" of the XML you're parsing. — Poni, Aug 14 '10 at 00:19

Mike Seymour · Answer 1 · 2010-08-14T11:13:10.467

Your're updating ingrediente at the start of each iteration, and then dereferencing it before you check that it's not null. This will give a segmentation fault if it is null. The loop should probably be structured along the lines of

for (ingrediente = first_ingrediente; 
     ingrediente; 
     ingrediente = ingrediente->NextSiblingElement("Ingrediente"))
    contador++;  
    if(ingrediente->Attribute("id"))
        id = atoi( ingrediente->Attribute("id") );  
    if(ingrediente->Attribute("categoria"))
        categoria = atoi ( ingrediente->Attribute("categoria") );  
    nombre = ingrediente->FirstChild()->ToText()->Value();  
}

Sorry for mixing some English into the variable names; I don't speak Spanish.

Or, if NextSiblingElement gives you the first element when you start iterating, the for can be replaced with while:

while ((ingrediente = ingrediente->NextSiblingElement("Ingrediente")))

The important point is to check for null after getting the pointer, and before dereferencing it.

Segmentation Fault using Tinyxml

1 Answers1