string array as function parameter fails in loop

[ZerMahlMeer]

Hallo,

I've got a weird issue here and I hope some one can help me finding the cause.

I have a function where I declared an array of strings (string_list). I pass the array to a function that does modifactions to the array. Whenn I address the string array index by index all values are stored properly. When I loop through the array incrementing the index automatically only the last index value will be stored in ALL positions.

Why is that? Or what am I doing wrong?

//this is the passing a string array to another function
int calling_function
{
      char *string_list[MAX_PATHNAME_LEN];  //< store strings in here
      function_called( string_list );  // passing a pointer to a string array
      return 0;
}

// this is the function receiving a reference to a string array to store data
int function_called( char* output_list[] )        
{
   int i = 0;  // counter variable 
   /*This works and the right values are stored in output_list*/
    output_list[0] = "02";
    output_list[1] = "12";
    output_list[2] = "22";
    output_list[3] = "32";
    output_list[4] = "42";
    output_list[5] = "52";
    output_list[6] = "622";
    output_list[7] = "72";

    /*this does not work and will store '31' in all places of the array*/
    while( i < 32 )
    {
        Fmt( sample, "%s<%d", i );  // increment value
        output_list[ i ] = sample;  // store value in index        
        i = i ++;                   // increment counter
    }
}

Thanks!

[Constantin--P · Accepted solution]

Hi,

When you do

output_list[ i ] = sample;

all of the members of the array have the same value: sample-a char pointer. You are afterwards modifying the contents of sample but the previous values still point to sample.

If you assign values to each array member like:

    output_list[0] = "02";
    output_list[1] = "12";
...

you assign different values: a pointer to a string containing "02", a pointer to a string contaning "12", ...

If you want to assign values in a loop you need to allocate memory for each string(output_list[i]) and copy the contents of sample in them.

Does this make sense to you?

Constantin

[ZerMahlMeer]

That makes somewhat sense! Thanks for your answer!

Edit: My summary .. your answer became 100% clear seconds after I replied!

So what I did was assigning the same pointer (a char array named sample) to all elements of  output_list. All elements pointed to the same direction in memory. When changing that memory location (sample) of course I changed all elements!