4.14. Debug Interface

The quirrel VM exposes a very simple debug interface that allows to easily built a full featured debugger. Through the functions sq_setdebughook and sq_setnativedebughook is possible in fact to set a callback function that will be called every time the VM executes an new line of a script or if a function get called/returns. The callback will pass as argument the current line the current source and the current function name (if any).:

SQUIRREL_API void sq_setdebughook(HSQUIRRELVM v);


SQUIRREL_API void sq_setnativedebughook(HSQUIRRELVM v,SQDEBUGHOOK hook);

The following code shows how a debug hook could look like(obviously is possible to implement this function in C as well).

function debughook(event_type, sourcefile, line, funcname) {

    local fname=funcname?funcname:"unknown"
    local srcfile=sourcefile?sourcefile:"unknown"
    switch (event_type) {
    case 'l': //called every line(that contains some code)
        println($"LINE line [{line}] func [{fname}] file [{srcfile}]")
    case 'c': //called when a function has been called
        println($"LINE line [{line}] func [{fname}] file [{srcfile}]")
    case 'r': //called when a function returns
        println($"LINE line [{line}] func [{fname}] file [{srcfile}]")

The parameter event_type can be ‘l’ ,’c’ or ‘r’ ; a hook with a ‘l’ event is called for each line that gets executed, ‘c’ every time a function gets called and ‘r’ every time a function returns.

A full-featured debugger always allows displaying local variables and calls stack. The call stack information are retrieved through sq_getstackinfos():

SQInteger sq_stackinfos(HSQUIRRELVM v,SQInteger level,SQStackInfos *si);

While the local variables info through sq_getlocal():

SQInteger sq_getlocal(HSQUIRRELVM v,SQUnsignedInteger level,SQUnsignedInteger nseq);

In order to receive line callbacks the scripts have to be compiled with debug infos enabled this is done through sq_enabledebuginfo();

void sq_enabledebuginfo(HSQUIRRELVM v, SQInteger debuginfo);