Question

I’m using malloc to make an error check of whether memory can be allocated or not for the particular array z1. ARRAY_SIZE is a predefined with a numerical value. I use casting as I’ve read it’s safe to do so.

long double *z1 = (long double *)malloc(sizeof (long double) * ARRAY_SIZE);  
if(z1 == NULL){  
   printf("Out of memory\n");  
   exit(-1);  
}

The above is just a snippet of my code, but when I add the error checking part (contained in the if statement above), I get a lot of compile time errors with visual studio 2008. It is this error checking part that’s generating all the errors. What am I doing wrong?

On a related issue with malloc, I understand that the memory needs to be deallocated/freed after the variable/array z1 has been used. For the array z1, I use:

free(z1);
z1 = NULL;

Is the second line z1 = NULL necessary?

I get 102 errors…well MVS2008 stops the errors at 102. The errors are of type:

error C2143: syntax error : missing ';' before 'type'  
error C2065: 'L' : undeclared identifier
// this error repeats for all my identifiers

and this points right after the closing } in the if statement.

ARRAY_SIZE is quite large. I define it as

#define ARRAY_SIZE 2500001

My full above code is too long. But I have a smaller code which is giving me the same behavior. Sorry for the formatting. I can’t seem to get it right.

#include stdio.h //note I have the actual < > in my code
#include stdlib.h
#include math.h
#define ARRAY_SIZE 11
#define VECTOR_SIZE 5

main()
{
    long double *z = (long double*) malloc(sizeof (long double) * ARRAY_SIZE);
    if(z == NULL){
        printf("Out of memory\n");
        exit(-1);
    }

    long double *k = (long double*) malloc(sizeof (long double) * VECTOR_SIZE);
    int i;
    long double A, B;
    void f(long double fa[], long double fb[], long double fA, long double fB);

    A = 0.5;
    B = 2;

    for(i = 0; i < VECTOR_SIZE; i++){
        k[i] = 0;
    }

    k[1] = 4;
    k[2] = 8;

    for(i = 0; i < ARRAY_SIZE; i++){
        z[i] = 0;
    }

    z[1] = 5;


    f(k, z, A, B);

    free(z);
    free(k);
    z = NULL;
    k = NULL;
}


void f(fa, fb, fA, fB)
long double fa[], fb[], fA, fB;
{
    fa[0] = fb[1]* fA;
    fa[1] = fa[1] - 1;
    fb[0] = 2* fB - fa[2];
    printf("fa[2] is 8 and is the same as *[fa + 2] and is  %3.3Le\n", *(fa + 2));
    printf("\nAddress of &fa[2] is %x\n", &fa[2]);
    printf("same address is fa + 2 is %x\n", fa + 2);
    return;
}

Answer 1

Problems in your code

Allright. Now that you’ve provided all the code it’s easier to explain your problems:

1. You’re trying to define variables "in the middle" of your functions. C doesn’t allow this. you have to define all your variables right at the start. That’s what’s giving you the
   error C2143: syntax error : missing ';' before 'type'
   errors.
2. Same goes for the function declaration (needs to be at the top of the function).

Therefore, changing your code to the following makes it work:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define ARRAY_SIZE 11
#define VECTOR_SIZE 5

main() {
    void f(long double fa[], long double fb[], long double fA, long double fB);

    long double* z = (long double*) malloc(sizeof (long double) * ARRAY_SIZE);
    long double* k = (long double*) malloc(sizeof (long double) * VECTOR_SIZE);
    int i;
    long double A, B;

    if (z == NULL) {
        printf("Out of memory\n");
        exit(-1);
    }

    A = 0.5;
    B = 2;

    for (i = 0; i < VECTOR_SIZE; i++) {
        k[i] = 0;
    }

    k[1] = 4;
    k[2] = 8;
    
    for (i = 0; i < ARRAY_SIZE; i++) {
        z[i] = 0;
    }
    
    z[1] = 5;
    
    f(k, z, A, B);
    
    free(z);
    free(k);
    z = NULL;
    k = NULL;
}

void f(fa, fb, fA, fB)  
long double fa[], fb[], fA, fB;  
{
    fa[0] = fb[1]* fA;
    fa[1] = fa[1] - 1;
    fb[0] = 2* fB - fa[2];
    
    printf("fa[2] is 8 and is the same as *[fa + 2] and is  %3.3Le\n", *(fa + 2));
    printf("\nAddress of &fa[2] is %x\n", &fa[2]);
    printf("same address is fa + 2 is %x\n", fa + 2);
    
    return;
}

A few other points

Now I’ll add a few more tips, that perhaps aren’t strictly errors (meaning, they still compile…), but aren’t very good coding practices:

1. As I said before, use consts to define constants rather than #defines.
2. define main() properly – that is int main() {... rather than just main() without a return type. It works in C, but doesn’t work in C++ and I consider it bad style. (Why the hell am I supposed to assume functions return int if nothing else is said? why not void?)
3. Following that, you should explicitly return a value from main().
4. I prefer declaring the void f(long double fa[], long double fb[], long double fA, long double fB); function prototype outside main().
5. When defining functions use the modern syntax – the one you used in the prototype – rather than the ancient one:
   void f(fa, fb, fA, fB)
long double fa[], fb[], fA, fB;
{
   Should become:
   void f(long double fa[], long double fb[], long double fA, long double fB) {.

This way your code turns to:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void f(long double fa[], long double fb[], long double fA, long double fB);

int main() {
    const int ARRAY_SIZE = 11;
    const int VECTOR_SIZE = 5;

    long double* z = (long double*) malloc(sizeof (long double) * ARRAY_SIZE);
    long double* k = (long double*) malloc(sizeof (long double) * VECTOR_SIZE);

    int i;
    long double A, B;

    if (z == NULL) {
        printf("Out of memory\n");
        exit(-1);
    }

    A = 0.5;
    B = 2;

    for (i = 0; i < VECTOR_SIZE; i++) {
        k[i] = 0;
    }

    k[1] = 4;
    k[2] = 8;
    
    for (i = 0; i < ARRAY_SIZE; i++) {
        z[i] = 0;
    }
    
    z[1] = 5;
    
    f(k, z, A, B);
    
    free(z);
    free(k);
    z = NULL;
    k = NULL;

    return 0;
}

void f(long double fa[], long double fb[], long double fA, long double fB) {
    fa[0] = fb[1]* fA;
    fa[1] = fa[1] - 1;
    fb[0] = 2* fB - fa[2];
    
    printf("fa[2] is 8 and is the same as *[fa + 2] and is  %3.3Le\n", *(fa + 2));
    printf("\nAddress of &fa[2] is %x\n", &fa[2]);
    printf("same address is fa + 2 is %x\n", fa + 2);
    
    return;
}  

Which I think is better.

First Post

Please provide all your code. I tested the following code on Visual C++ 2008 Express with "language extensions" disabled and level 4 warnings. It works just fine:

#include <stdlib.h>
#include <stdio.h>

int main() {
    const int ARRAY_SIZE = 1024*1024;

    long double *z1 = (long double *)malloc(sizeof (long double) * ARRAY_SIZE);
    if (z1 == NULL) {
        printf("Out of memory\r\n");
        exit(-1);
    }

    printf("Awesome!\r\n");

    return 0;
}

Maybe you forgot an include, maybe you did something else wrong. The code snippet itself seems perfectly fine. The second error you described seems totally unrelated:
error C2065: 'L' : undeclared identifier // this error repeats for all my identifiers

By the way, prefer const over #define.