memory not valid

[Gast]

Hello, I made a program which runs fine for one or two times (after a reboot of miniserver), but then gets a memory not valid error. Does anybody see why?

char *l;
while (l==l)
{
char *value;
char *result = httpget("api.wunderground.com","/api/apikey/alerts/conditions/forecast/hourly/long%3ADL/pws%3A1/bestfct%3A1/q/gent,belgium.json");
value = strstrskip(result, "city":"");
char *substringg = calloc(1, 15);
char *newsubstring= calloc(1, 150);
strncpy(substringg,value,1);
char *breakout = """;
while (strcmp(substringg, breakout) != 0)
{
//printf("substringresultn = %s", substringg );
strcat(newsubstring, substringg);
//printf("newsubstringresultn = %s", newsubstring );
value = strstrskip(value,substringg);
free(substringg);
strncpy(substringg,value,1);
}
setoutputtext(0, newsubstring);
free(value);
free(substringg);
free(result);
free(newsubstring);
free(breakout);
sleeps(10);
printf("weer opgehaald");
}

Thanks.

[Christian Fenzl]

There is a ready solution for querying the Wunderground weather data in this thread:

https://www.loxforum.com/forum/faqs-tutorials-howto-s/1049-howto-wunderground-api-in-programm-baustein-abfragen

[Gast]

Yep, I saw that one, thanks, but it wasn't the service as such that was important for me, it was to learn the program block/code. It could have been any other service. I wonder why it works 2 times and then raises an error. When I reboot the miniserver it works again for 2 times.

[simon_hh]

Hi Prince,
I am not sure, because I do not use pico c programs, but what I see is, that you allocate "char *result" but you never free it later on. So maybe there is a buffer overflow.
I don´t know if the server has any garbage collector or automatic free for memory.
Try free(result) in the last slope before "sleep"

Hi Simon, thanks for the feedback, but I free "result" (between free(substringg); and free(newsubstring). I tried to move it to just before "sleep" but same result.

[Robert L.]

there is a Free(result)

i think the Problem is:

free(substringg);
strncpy(substringg,value,1);

Thanks Robert, I'll have a look at this.

[Christian Fenzl]

My C skills seem to be also far away, but it might be a problem that you redefine variables on every loop (char *value; char *result ...)
Possibly define the variables (pointers) outside the loop, and address them as normal variables/pointers inside.

[Christian Fenzl]

Nope, this is not the problem. Also C can handle this.

[Robert L.]

wolltest du mir antworten?

http://www.cplusplus.com/reference/cstring/strncpy/

i still think Free the "substringg" is the problem
strncpy expects a string that is at least num (+1?) long..

[Christian Fenzl]

Robert L. Nein, ich hab mich selbst korrigiert, das Wieder-initialisieren einer Variable in einer Schleife funktioniert auch in C.

[Christian Fenzl]

char *l;
while (l==l)

of course is a strange construct, why not simply (1==1)?
But it won't fix the error.

[Christian Fenzl]

Another issue (that I don't know if PicoC handles different, but C++/C# needs) is escaping of quotes:

value = strstrskip(result, "city":"");
--> value = strstrskip(result, "city\":\"");

char *breakout = """;
--> char *breakout = "\"";

Hi Christian, I must have been lost in the copy but the quotes are escaped indeed

[Gast]

I deleted all the free(); things and now it works every time... (except free(result1))
Finally I added a push button to it and this version has no memory issue.(copied from the example Christian pasted)

int nEvents;
float fEingangEins;
char *host="api.wunderground.com";
char *page="/api/xx/alerts/conditions/forecast/hourly/long%3ADL/pws%3A1/bestfct%3A1/q/gent,belgium.json";
char *breakout = "\"";
while(1==1){
    nEvents = getinputevent();  //Eingänge auslesen.
    if (nEvents & 0x18){               // Bitmaske für die Eingang.
        fEingangEins = getinput(0); // Eingänge auf Veränderung prüfen, und ggf. Variabeln aktualisieren.
    }
    if (fEingangEins != 0){
        setoutputtext(0, "ophalen gemeente..");
        fEingangEins = 0; // 0 setzten, damit der Abruf pro Flanke nur einmal erfolgt.    
        char *value;
        char *result1 = httpget(host,page);
        printf("t");
        value = strstrskip(result1, "city\":\"");
        free(result1);
        char *substringg = calloc(1, 15);
        char *newsubstring= calloc(1, 15);
        strncpy(substringg,value,1);
        while (strcmp(substringg, breakout) != 0) 
            {
                printf("substringresultn = %s", substringg );
                strcat(newsubstring, substringg);
                //printf("newsubstringresultn = %s", newsubstring );
                value = strstrskip(value,substringg);
                strncpy(substringg,value,1);
            }
        setoutputtext(0, newsubstring);    
        printf("weer opgehaald");
        sleeps(10);
    }
}