Dynamic array inside struct and malloc fail

Question

Consider the following abstracted code that reads some bytes from a file:

typedef struct A{
int size;
char * dataArray;
}A

A load(char* filename, int inSize)
{
    A newA;
    newA.size = inSize;
    FILE *filePtr;
    filePtr = fopen(filename,"rb");

    char buff[1];
    int i = 0;

    newA.dataArray = ( char*)malloc(sizeof(char) * newA.size);
    for (i = 0; i < newA.size; i++)
    {
        fread(buff, sizeof(char), 1, filePtr);
        newA.dataArray[i] = buff[0];
    }

    char* copyOfDataArray = (char*)malloc(sizeof(char) * newA.size);

    for (i = 0; i < newA.size; i++)
    {
        fread(buff, sizeof(char), 1, filePtr);
        copyOfDataArray[i] = newA.dataArray[i];
    }

    newA.dataArray = copyOfDataArray;
    return newA
}

void Initialize()
{
    A first = load("file1", 100);
    A second = load("file2", 20);
}

Both calls to function load return the expected result (data array has the same bytes as the file). Variables first and second are never used again.

However after a couple of hundreds lines of code the program always crashes with:

*malloc.c:2451: sYSMALLOC: Assertion '(old_top == (..... failed.*

The crash always occurs on the same line of code, but that line has nothing to do with variables first, second or even with struct A whatsoever.

My question is : is my way of instancing and loading 'first' and 'second' wrong? Can it cause some kind of memory leak / memory overflow that crashes the program long after the load function has finished?

Bonus : The crash does not occur if I only load "file1", as soon as i load both "file1" and "file2" the crash reappears.

Sorry for the long question.

Answer 1

You have memory leaks there. You have to free the previously allocated memory in newA.dataArray, before you assign there a new memory.

As stated by Joachim, read operation is very time consuming and you shall read data in blocks to minimize overhead.

Additionally, you have to close file descriptors, otherwise they will be depleted soon.

Answer 2

There are many issue on the code as already given by others. Please checks bellow

typedef struct A{
int size;
char * dataArray;
}A

A load(char* filename, int inSize)
{
    A newA;
    newA.size = inSize;
    FILE *filePtr = NULL ; //Use NULL 
    char buff[1]; //Size of buffer is only 1 ,If needed increase that to copy more at a time
    int i = 0;

filePtr = fopen(filename,"rb");    
//Try to check for the filePtr == NULL or not

newA.dataArray = ( char*)malloc(sizeof(char) * newA.size);
//Same checking should be done here

for (i = 0; i < size; i++) //What is size 
{
    fread(buff, sizeof(char), 1, filePtr);
    newA.dataArray[i] = char[0]; //What is char[0]
}
//instead this you can read the bytes in a single call, use that.
// fread(buff, sizeof(char), <size to read >, filePtr);

char* copyOfDataArray = (char*)malloc(sizeof(char) * newA.size);

for (i = 0; i < size; i++)
{
    fread(buff, sizeof(char), 1, filePtr);
    copyOfDataArray[i] = newA.dataArray[i];
}

//why reading again once you done above.
newA.dataArray = copyOfDataArray;

return newA; //Please check: How you can return a auto variable.
}
void Initialize()
{
    A first = load("file1", 100);
    A second = load("file2", 20);
}