Question

I want to remove the last new line from the following function:

void WriteToFile(node *tree)
{
    void Write(node*);
    fp = fopen("dictionary.txt","w");
    if(fp==NULL)
    {
        printf("Cannot open file for writing data...");
    }
    else //if(tree==NULL)
    {
        if(tree!=NULL)
        {
            Write(tree);
        }
        fclose(fp);  
    }
}
void Write(node *tree)
{
    if(tree!=NULL)
    {
        fprintf(fp,"%s:%s\n",tree->word,tree->meaning);
        Write(tree->left);
        Write(tree->right);
    }
}

I am using this function to write to a text file the contents of a BST, and I dont want it to write the last new line, how can I remove it?

Answer 1

In a recursive routine like yours, you cannot easily know which is the last call, but you can know what is the first call.

Rather than writing data and, optionally, a newline, consider writing an optional newline followed by data:

void FirstWrite(node *tree, FILE *fp)
{
    if (tree)
    {
        fprintf(fp, "%s%s", tree->word, tree->meaning);
        Write(tree->left, fp);
        Write(tree->right, fp);
    }
}
void Write(node *tree, FILE *fp)
{
    if (tree)
    {
        fprintf(fp, "\n%s%s", tree->word, tree->meaning);
        Write(tree->left, fp);
        Write(tree->right, fp);
    }
}

But consider the most used definition of a line for text mode files is: a sequence of 0 or more characters folllowed by and including a newline. According to this definitilon all lines have a newline; and the last piece of data in your file is not a line.

^{At least one badly written program I’ve used fails to process the whole input because of that. My guess is that it does something like}

fgets(buf, sizeof buf, inf);
inlen = strlen(buf);
if (buf[inlen - 1] == '\n') processline(buf);

^{This badly written program would work if the last piece of data included a newline.}