Passing Strings through Structs

Question

So I've got a struct called stationInfo, which has a bunch of info, including latitude, longitude, and station ID. I have written a function that will puts reads from a file and stores the values into arrays of structs. Now, I want to move those arrays of structs into another array of structs.

MapMarker mapInfo[t];
int k;
for(k=0; k < MAX_STATIONS; k++){
    mapInfo[k].location.latitude = stationInfo[k].location.latitude;
    mapInfo[k].location.longitude = stationInfo[k].location.longitude;
    char* stationName = getStationName(stationInfo[k].stationID);
    strcpy(mapInfo[k].markerName, stationName);
}

However, this is breaking my program. How can I fix this?

EDIT: As per Paddy's request:

mapMarker Struct:

typedef struct{
GeographicPoint location;
char markerName[100];
char markerText[1000];
int type;
} MapMarker;

GeographicPoint location is split into a latitude and logitude struct.

char* getStationName(int stationID){
if (stationID < 0 || stationID >= MAX_STATIONS || !AllStationNames[stationID])
    return "Unknown";
return AllStationNames[stationID];
} /* getStationName */

And the Array

char *AllStationNames[MAX_STATIONS] = {
[1] = "Ian Stewart Complex/Mt. Douglas High School",
[3] = "Strawberry Vale Elementary School",
...
[197] = "RASC Victoria Centre",
[199] = "Trial Island Lightstation",
[200] = "Longacre",
};

Show your MapMarker struct definition. Also, you should show getStationName. — paddy
– paddy, Commented Nov 12, 2013 at 3:29
What is the value of t you are using for the VLA declaration of mapInfo? Surely you meant to use MAX_STATIONS. — paddy
– paddy, Commented Nov 12, 2013 at 3:36
I was going to use MAX_STATIONS, but I thought that t gives me the ammount of stations I truely have, so why declare any more than that. But now that I look at it, its probably just better to have it as MAX_STATIONS. — Jake Cooper
– Jake Cooper, Commented Nov 12, 2013 at 3:39
Well, if t can be less than MAX_STATIONS, you will have a buffer overrun. I don't see anything wrong with the strcpy. Using strncpy is safer, but I think the problem is mismatching the array size with the number of elements you are writing to. Of course, you could just loop to t instead of MAX_STATIONS. — paddy
– paddy, Commented Nov 12, 2013 at 3:41

paddy · Accepted Answer · 2013-11-12 04:15:42Z

1

As discussed in comments, you are declaring a VLA (variable-length array) using the variable t as size. That is always less than or equal to MAX_STATIONS. So you have a buffer overrun issue.

MapMarker mapInfo[t];
int k;
for(k=0; k < MAX_STATIONS; k++){
    // Accessing mapInfo[k] when k >= t will have undefined behaviour
}

The simplest solution is to make mapInfo constant-size and loop to t:

MapMarker mapInfo[MAX_STATIONS];
for( k = 0; k < t; k++ ) ...

answered Nov 12, 2013 at 4:15

paddy

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