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[Tinycc-devel] C language modification using TinyCC - problems

From: James Dunne
Subject: [Tinycc-devel] C language modification using TinyCC - problems
Date: Thu, 19 May 2005 23:58:07 -0500


I'd just like to say thank you for TinyCC - I've had much pleasure
playing around with it so far!

I wanted to make a few simple changes to the C language just for fun,
but I came across some problems that I can't figure out:

Use the binary '~' operator for char * concatenations.  All I want it
to do is to check for two char *s on either side and return the value
called by:

char *__concat(char *a, char *b);

I've gotten the '~' operator to co-exist as both a binary and unary
operator - named TOK_CAT, and TOK_A_CAT for ~= operations.  I've added
the operator to the expr_shift() function and have defined TOK_CAT and
TOK_A_CAT correctly.  My problem becomes the function call portion.

In gen_op() I've modified the "if (bt1 == VT_PTR && bt2 == VT_PTR)"
block to allow for "if (op == TOK_CAT)" inside it so that I can
implement it there.  I've defined the operator to only work on two
(char *)s.  This is the relative block of code that I have "somewhat"
working now:

        /* if both pointers, then it must be the '-' op */
        if (bt1 == VT_PTR && bt2 == VT_PTR) {
                        /* get the pointed-to types */
                        pt1 = pointed_type(&vtop[-1].type)->t;
                        pt2 = pointed_type(&vtop[ 0].type)->t;
                        pbt1 = pt1 & VT_BTYPE;
                        pbt2 = pt2 & VT_BTYPE;

                        /* string concatenation operator */
                        if (op == TOK_CAT) {

                                /* generate function call */
                                vpush_global_sym(&func_old_type, TOK___concat);

                                /* return value */
                                vtop->r = RC_IRET;

                        } else if (op == '-') {

My problem is the return value of the function call.  The parameters
passed in to my function work correctly, but I cannot get the correct
return value to be used.  Here's my sample program:

char *__concat(char *a, char *b) {
        char    *result = (char *)malloc(strlen(a) + strlen(b) + 1);
        printf("%s\n", a);
        printf("%s\n", b);
        strcpy(result, a);
        strcat(result, b);
        printf("%s\n", result);
        return result;

int main(int argc, char **argv) {
        char    *s1 = "hi ";
        char    *s2 = "neat!";
        char    *s3 = "poo";

        printf("s1 %p\n", s1);
        printf("s2 %p\n", s2);
        printf("s3 %p\n", s3);

        s3 = s1 ~ s2;   // line 20

        printf("s1 %p\n", s1);
        printf("s2 %p\n", s2);
        printf("s3 %p\n", s3);

        return 0;

My outputs are the following:

ex6.c:20: warning: assignment makes pointer from integer without a cast
s1 0x807eb6c
s2 0x807eb70
s3 0x807eb76
hi neat!
s1 0x807eb6c
s2 0x807eb70
s3 0xbffff5cc

What am I doing wrong?  s3's value looks wrong and produces the same
garbage string each time the program runs.  As you can see, __concat
is getting the parameters correct and successfully concatenates them. 
The generated code, however, does not process the return type
correctly.  I hope it's a small, easy fix!  =)

James Dunne

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