[Mapserver-dev] Trouble with pointers to strings in mapserver

[woodbri at swoodbridge.com]

Sean,

based on what you have described, I would recommend a make clean; 
make and try it again. When pointers "magically" change from the 
outside of a function all to the inside, it indicates that you have 
obj files out of sync with one another and or the source. This could 
be because you changed a header and did not recompile everything that 
referenced it or that you are pulling in an object from a library 
that is out of date or the like.

-Steve W.

On 7 Feb 2003 at 11:51, Sean Gillies wrote:

> Hi all,
> 
> I have adopted (through Bugzilla) the request for a msCopyMap function
> and am having problems with the string properties of the objects.  I'm
> looking for some advice on the proper solution within the context of
> the existing mapserver code.
> 
> The code I'm testing for msCopyMap starts like this:
> 
> 
> int msCopyMap(mapObj *dstMap, mapObj *srcMap) {
>    ...
>    copyStringProperty(dstMap->name, srcMap->name);
>    copyProperty(&(dstMap->status), &(srcMap->status), sizeof(int));
>    ...
> }
> 
> void copyProperty(void *dst, void *src, int size) {
>    if (src == NULL) dst = NULL;
>    else memcpy(dst, src, size);
> }
> 
> void copyStringProperty(char *dst, char *src) {
>    if (src == NULL) dst = NULL;
>    else {
>      if (dst == NULL) dst = strdup(src);
>      else strcpy(dst, src);
>    }
> }
> 
> 
> I am using functions that test for NULL pointers and wrap memcpy
> and strcpy.  This code is working as I expect.  Map names and
> numeric properties are copied.
> 
> Next, I have started to write a msCopyLayer function which looks
> like:
> 
> 
> int msCopyLayer(layerObj *dstLayer, layerObj *srcLayer) {
>    ...
>    copyProperty(&(dstLayer->index), &(srcLayer->index), sizeof(int));
>    copyProperty(&(dstLayer->map), &(srcLayer->map), sizeof(mapObj *));
>    copyStringProperty(dstLayer->classitem, srcLayer->classitem); ...
> }
> 
> 
> and I call this function from msCopyMap like:
> 
> 
> int msCopyMap(mapObj *dstMap, mapObj *srcMap) {
>    ...
>    copyStringProperty(dstMap->name, srcMap->name);
>    copyProperty(&(dstMap->status), &(srcMap->status), sizeof(int));
>    copyProperty(&(dstMap->height), &(srcMap->height), sizeof(int));
>    copyProperty(&(dstMap->width), &(srcMap->width), sizeof(int));
> 
>    copyProperty(&(dstMap->numlayers), &(srcMap->numlayers),
>    sizeof(int));
> 
>    for (i = 0; i < dstMap->numlayers; i++) {
>      initLayer(&(dstMap->layers[i]), dstMap);
>      msCopyLayer(&(dstMap->layers[i]), &(srcMap->layers[i]));
>    }
>    ...
> }
> 
> 
> The problem I experience is that copyStringProperty() isn't working
> within msCopyLayer().  I stepped through the code using gdb and
> discovered that when copyStringProperty() is called within
> msCopyLayer(), the source string passed to copyStringProperty is being
> nullified.
> 
> For example, in msCopyLayer, before this line
> 
>    copyStringProperty(dstLayer->classitem, srcLayer->classitem);
> 
> is executed, I have srcLayer->classitem = "CO08_D00_".  Inside
> copyStringProperty, I have src = 0x0.
> 
> I'm stumped, and wishing that I was more of a real programmer and less
> of a hacker.  Why does copyStringProperty() work when called in
> msCopyMap(), but not in msCopyLayer()?  I have found one solution and
> that is to not call copyStringProperty() from msCopyLayer, but instead
> copy its code explicitly into msCopyLayer.  I'd rather not if it
> wasn't necessary. I've looked through the rest of the MapServer code
> and the only similiar code I found is in loadLayer() where we have
> 
>    layer->name = getString()
> 
> getString is using the global string msyytext, and returning
> 
>    return(strdup(msyytext))
> 
> but I don't think I should be using a global in msCopyMap.
> 
> Grateful for any advice,
> Sean
> 
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