understanding array declaration

[kokoilie]

Hello,
I was hoping I can declare a variable sized array but the debugger gives an error which I can't understand how to fix...

  int vindex[vn];

the variable vn is already declared and given a value.


I recently started coding in c++ and I am self taught in c++ and "AutoIt3" languages and in autoit declaring such array is acceptable.

[chicofeo]

Could you post the error (word by word) from the debugger? or post your code.

#include <iostream>

int main()
{
    int list[] = { 1,2,3,4,5,6,7,8,9,10 }; //Declare and initialize the array.

    for (auto value : list) // Use the range for (C++11) to iterate thru the array.
	   std::cout << value << "\t";
 
    std::cout << std::endl;

    for (int count = 0; count < 10; count++) // Or use the for loop to iterate thru the array.
	   std::cout << list[count] << "\t";

    return 0;
}

[Peter87]

C++ doesn't have variable-length arrays. You can use std::vector instead.

std::vector<int> vindex(vn);

http://www.cplusplus.com/reference/vector/vector/

[kokoilie]

The idea is to read a binary file and depending on how many integers there are (count is mentioned in the file's header) to have an array with that size

#include <cstdlib>
#include <iostream>
#include <array>

using namespace std;


int main(int argc, char *argv[])
{
    FILE *model,*skin,*output;
    float pos[3];
    unsigned int vn=0,vofs=0, triendofs=0, trin=0, triofs=0, c=0, vindexofs, namel, nameofs;
    char name;
    uint16_t tripos[3];
    
    printf("\n");
    if(argc < 4)
    {
            printf("Error. Expected 3 filepath arguments.\n");
            return 1;
    }
    output = fopen(argv[3],"r");
    if(output != NULL)
    {
           printf("Output file exists. Overwrite? Y/N:");
           while (c != 121)
           {
                 c = getchar();
                 if (c == 110)
                 {
                     printf("\nOk, (sad)\n");
                     fclose(output);
                     return 1; 
                 }
           }       
    }
    fclose(output);
    model = fopen(argv[1],"rb");
    if(model == NULL)
    {
            printf("Unable to open model file.\n");
            return 1;
    }
    skin = fopen(argv[2],"rb");
    if(skin == NULL)
    {
            printf("Unable to open skin file.\n");
            fclose(skin);
            return 1;
    }
    output = fopen(argv[3],"wt");
    if(output == NULL)
    {
           printf("Unable to create output file.\n");
           fclose(model);
           fclose(skin);
           return 1;   
    }
    if(fseek(model,0x8,SEEK_SET))
    {
           printf("Seek error: model file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;  
    }
    if(!fread(&namel,4,1,model))
    {
         printf("Error: unable to read model name length.\n");
         fclose(model);
         fclose(skin);
         fclose(output);
         return 1;
    }          
    if(!fread(&nameofs,4,1,model))
    {
         printf("Error: unable to read model name offset.\n");
         fclose(model);
         fclose(skin);
         fclose(output);
         return 1;
    }
    if(fseek(model,nameofs,SEEK_SET))
    {
           printf("Seek error: model file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;  
    }
    if(!fread(&name,namel,1,model))
    {
          printf("Error: unable to read name char %d.\n", namel);
          fclose(model);
          fclose(skin);
          fclose(output);
          return 1;
    }
    printf ("%s\n", name);      
    if(fseek(model,0x3C,SEEK_SET))
    {
           printf("Seek error: model file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;  
    }
    if(!fread(&vn,4,1,model))
    {
         printf("Error: unable to read vert count.\n");
         fclose(model);
         fclose(skin);
         fclose(output);
         return 1;
    }
    int vindex[vn];
    vindex[0] = vn;
    //here is where I'll add the code to read the indexes.             
    if(!fread(&vofs,4,1,model))
    {
         printf("Error: unable to read vert offset.\n");
         fclose(model);
         fclose(skin);
         fclose(output);
         return 1;
    }
    
    fprintf(output, "#test file\ng default\n");
    if(fseek(model,vofs,SEEK_SET))
    {
           printf("Seek error: model file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;  
    }
    while(vn -- )
    {
           if(fread(&pos,4,3,model) == 3)
           {
                 fprintf(output,"v %f %f %f\n",pos[0],pos[1],pos[2]);    
           }
           else 
           {
                 printf("Error: unable to read/write vert position number %d.\n", vn);
                 break;
           }
           if(fseek(model,36,SEEK_CUR))
           {
                 printf("EOF or error.\n");
                 break;
           }
    }
    vn = vindex[0];
    
    if(fseek(skin,vindexofs,SEEK_SET))
    {
           printf("Seek error: model file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;  
    }
    while(vn -- )
    {
           if(fread(&pos,4,3,model) == 3)
           {
                 fprintf(output,"v %f %f %f\n",pos[0],pos[1],pos[2]);    
           }
           else 
           {
                 printf("Error: unable to read/write vert position number %d.\n", vn);
                 break;
           }
           if(fseek(model,36,SEEK_CUR))
           {
                 printf("EOF or error.\n");
                 break;
           }
    }
    if(fseek(skin,0x10,SEEK_SET))
    {
           printf("Seek error: skin file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;  
    }
    if(!fread(&triofs,4,1,skin))
    {
           printf("Error: unable to read triangle offset.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;
    }
    if(fseek(skin,0x4,SEEK_CUR))
    {
           printf("Seek error: skin file too short.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;
    }
    if(!fread(&triendofs,4,1,skin))
    {
           printf("Error: unable to read triangle count.\n");
           fclose(model);
           fclose(skin);
           fclose(output);
           return 1;
    }
    trin=(triendofs-triofs)/6;
    //trin = trin / 3;
    fprintf(output,"g %s\n", name);
    if(fseek(skin,triofs,SEEK_SET))
    {
           printf("Seek error: skin file too short.\n");
           fclose(model);
           fclose(output);
           return 1;  
    }
    
    while(trin -- )
    {

            if(fread(&tripos,2,3,skin) == 3)
            {
                 fprintf(output,"f %d %d %d\n",tripos[0]+1,tripos[1]+1,tripos[2]+1);
            }
            else 
            {
                 printf("Error: unable to read/write triangle number %d.\n",trin);
                 break;
            }
            
    }
    fclose(model);
    fclose(skin);
    fclose(output);
    printf("\n");
    return EXIT_SUCCESS;
} 

This code somewhat works but I need to find a way to make that array to fix the output.
Edit: I can't post the error because the compiler is not saying exactly what is the problem but since this is the only thing I added after it worked it has to be the problem.

[rabster]

It looks like your initializing an array with a value of 0 elements so it can not hold anything. Change your variable vn to 1 and then you are able to initialize the array with 1 element.

#include <iostream>
using namespace std;

int main() {
    int vn = 1;
    int someArray[vn];
    someArray[0] = 1; //Index 0 is still the first starting point.
}

I think that might be the problem.

[kokoilie]

Actually the value is later changed from 0 to
fread(&vn,4,1,model)
which in the example file I'm using is 9156
Also Peter87 said that I can't declare an array with variable that way.

[rabster]

Oh then just allocate the memory to the array then. I brain farted but if you want a run time array you need to to do this. Although I swear you could initialize an array to a value in a variable as long as it never changed in value and happened at compile time, although I could be wrong.

#include <iostream>
using namespace std;

int main() {
    int vn;
    cin >> vn;
    int *someArray = new int[vn]; //Makes a run time array by allocating memory
    delete[] someArray; //Deletes the array to free up memory/prevent mem leak
}

[kokoilie]

Thank you rabster,
this works like a charm and I hope I won't need any more help to finish this script.