Void pointer as struct array in C - c

Question

I was trying to use void pointer as Struct array to keep a few struct object together on disk.I want to write records to disk with using void pointer(think as a cluster consist of records).
void addRecordToDataPage(City record)
{
void* data = malloc(sizeof(City)*RECORD_COUNT);
FILE* fp;
fp=fopen("sampledata2.dat", "rb");
City pageofCity [RECORD_COUNT]; //City is my Struct.
if(!fp) //if it is first access, put the record to pageofCity[0]..
{
pageofCity[0]=record;
data=pageofCity;
writeDataPageToDisk(data); ..and call the write func.
return;
}
fread(&data, sizeof(City)*RECORD_COUNT, 1, fp);
int i=0;
while( (City *)data )
{
pageofCity[i] = ((City *)data)[i];
i++;
}
pageofCity[i]=record;
}
//and this is my writer function.
void writeDataPageToDisk(void* dataPage)
{
FILE* fp;
fp=fopen("sampledata2.dat", "a");
if(!fp)
{
fp=fopen("sampledata2.dat", "wb");
writeDataPageToDisk(dataPage);
}
fwrite(dataPage, sizeof(City)*RECORD_COUNT,1,fp);
fclose(fp);
}
in the line of pageofCity[i] = ((City *)data)[i]; I got an memory error.
This is my first question in this website, please forgive me about my errors :).

Answer 1

There are multiple issues with your code.
The most likely cause for your error looks like:
while( (City *)data )
The value of data never changes and you are continuously reading a memory a byte ahead each time in the loop.
if (!fp)
{
int recordsRead = fread(&data, sizeof(City), READ_COUNT, fp);
int i=0;
while( i < recordsRead)
{
}
}
pageOfCity[recordsRead] = record;
Also since you are appending one extra element to your array you will need to declare the extra space for that record.
City pageofCity [RECORD_COUNT + 1]; //City is my Struct.