C - Malloc导致程序崩溃

Question

I am writing this C code which takes in a file and reads in values from it, the code doesn't do anything yet, but this is what I have so far. The program is crashing in the block that is calling four mallocs. The program works fine if I comment out y, f, and yp. I don't know what it is causing it. So any help will be appreciated.

Note: I am testing this on ubuntu with gcc. And I did trying casting the malloc to "(float *)" but I still get the same error.

int main( int argc, char *argv[])
{
    FILE *rhs, *output;
    int niter, n, i = 0, j = 0, k = 0, n1 = n + 1;

    rhs = fopen(argv[1], "r");
    // ab+ opens file for writting and creates the file if need be
    output = fopen(argv[2], "ab+");
    niter = atoi(argv[3]);

    // check if files open up or not, if not exit.
    if((rhs == NULL) || (output == NULL))
    {
        printf("Error Opening files.\n");
        exit(1);
    }

    // read in N
    fscanf(rhs, "%d", &n);

    // THIS IS THE BLOCK CAUSING THE CRASH
    // CODE WORKS WHEN I COMMENT OUT LINES AND ONLY LEAVE ONE OF THEM IN
    // generate array to hold values from rhs file
    float *numbers = malloc(sizeof(float) * ((n1)*(n1)));
    float *y = malloc(sizeof(float) * ((n1)*(n1)));
    float *f = malloc(sizeof(float) * ((n1)*(n1)));
    float *yp = malloc(sizeof(float) * ((n1)*(n1)));

    // get numbers and store into array
    while(fscanf(rhs, "%f", &numbers[i]) != EOF)
    {
        printf("In while %f\n", numbers[i]);
        i++;
    }

    fclose(rhs);

    return 0;

}

Answer 1

One issue is:

You are initializing n1 with an uninitialized value from n :

int niter, n, i = 0, j = 0, k = 0, n1 = n + 1;
                                        ^
                                        +-- "n" is not initialized here, might have any value.
                                            thus, "n1" is also not initialized to a known value.

Therefore, your call to malloc most likely recieves a too large value to be allocated at all. Initialize "n1" after you have read "n":

// read in N
fscanf(rhs, "%d", &n);
n1 = n + 1;

In any case, it is worth checking the return value from malloc() to see if it returned NULL in case the memory could not be allocated.

Answer 2

The n1 contains a garbage at the moment of the malloc() call. Thus you simply try to allocate a HUGE amount of memory .

Answer 3

Check whether memory has been allocated successfully or not by checking the value of numbers, y, f, yp, if their value is NULL, then memory can't be allocated. How large is the value of n1?

Answer 4

It is because n1 is undefined at the point you call malloc() .

int niter, n, i = 0, j = 0, k = 0, n1 = n + 1;

The above line didn't initialize n , so n1 = n + 1 assigns an undefined value to n1 .

You may need to put n1 = n + 1; after fscanf(rhs, "%d", &n); .