Help wanted

Help wanted

[Jane Liang]

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Hi, all:

I have a simple program(see below), it ran without any problem in sun (with
sun's compiler). However, when I compiled it in gcc on PC, it crashed at
line 13.  I tried to use strtok and some other string functions but none of
them seems works fine.  Does anyone know why?

Thanks!

Jane


Line 1    #include <stdlib.h>
Line 2    #include <stdio.h>
Line 3    #include <string.h>
Line 4
Line 5    int main()
Line 6    {
Line 7
Line 8      char *str = "0.12000, 0.0, 0.0";
Line 9      char *ptr;
Line 10     float  num;
Line 11
Line 12     ptr = strchr(str, ',');
Line 13     *ptr = '\0';
Line 14 
Line 15     num = atof(str);
Line 16
Line 17     return 0;
Line 18   }



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Re: Help wanted

[Ben Davis]

On Monday 17 March 2003 4:26 pm, Jane Liang wrote:
> Line 8      char *str = "0.12000, 0.0, 0.0";

This is a constant string, so it is stored in read-only memory.

> Line 13     *ptr = '\0';

You are now writing to read-only memory. Hence the crash.

You can fix your code by making 'str' an array instead:

   char str[] = "0.12000, 0.0, 0.0";

Then the string will be stored temporarily on the stack, which is writable. 
The array will be just the right size to accommodate the string.

When using GCC, I recommend you compile with -Wwrite-strings. String constants 
will then be given the 'const' qualifier, and you will get a warning if you 
don't use 'const' yourself where necessary:

   const char *str = "0.12000, 0.0, 0.0";

Ben

RE: Help wanted

[Jane Liang]

Hi, Ben:

It works!

Thanks!
 
Jane


-----Original Message-----
From: Ben Davis [mailto:bnd25@cam.ac.uk] 
Sent: Monday, March 17, 2003 10:54 AM
To: Jane Liang; 'GCC-help'
Subject: Re: Help wanted


On Monday 17 March 2003 4:26 pm, Jane Liang wrote:
> Line 8      char *str = "0.12000, 0.0, 0.0";

This is a constant string, so it is stored in read-only memory.

> Line 13     *ptr = '\0';

You are now writing to read-only memory. Hence the crash.

You can fix your code by making 'str' an array instead:

   char str[] = "0.12000, 0.0, 0.0";

Then the string will be stored temporarily on the stack, which is writable. 
The array will be just the right size to accommodate the string.

When using GCC, I recommend you compile with -Wwrite-strings. String
constants 
will then be given the 'const' qualifier, and you will get a warning if you 
don't use 'const' yourself where necessary:

   const char *str = "0.12000, 0.0, 0.0";

Ben

help wanted

[rojesh p]

     The 8051 does not seem to have a GCC back end. we are trying 
to develop a backend one. where can we get the details about the 
rtl syntax(other than porting and using gcc). please help us.

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RE: help wanted

[Rupert Wood]

Danish Samad wrote:

> The GCC project I have downloaded is huge containing a lot of other
> compilers, assemblers etc. Can you please guide me where to find the
> gcc c compilers front end with documentation.

There's plenty of it, yes, but if you're going to attempt some heavy
backend wizardry then you will have to get your head around most of it
sooner or later.

Unless you have a merged gcc-binutils tree (not likely if you downloaded
it yourself) then you don't actually have any assemblers bundled.
Instead, you have

   /                 Top level makefiles for cygnus toolchain
   /gcc              C front end and generic backend
   /gcc/config       CPU/OS specific instruction sets and ABIs
   /gcc/cp           C++ front end
   /gcc/objc         Objective-C front end
   /gcc/f            Fortran front end
   /gcc/java         Java front end
   /gcc/po           Internationalization 'pot' translation files
   /gcc/intl         Internationalization library
   /gcc/fixinc       Fixes for non-standards-conformant system headers
   /gcc/doc          Documentation
   /gcc/ginclude     GCC build includes
   /gcc/testsuite    GCC regression testsuite

etc. plus a number of runtime libraries and helper libraries (libiberty)
at the top level.

i.e. you'll find the C-front end and the generic backend in the gcc
directory, plus you'll need one of the machine description files (.md)
plus a number of headers and source files in the config tree to tell the
generic backend how to generate processor specific code.

All documentation is build with GCC into at least .info format. It is
also available online at http://gcc.gnu.org/onlinedocs/

Good luck!

Rup.

help wanted

[Danish Samad]

hello

I have been assigned the task to design and develop an
optimizing C compiler which generates instructions
capable of executing in parallel. For this purpose we
have decided to use gcc c compiler front end and
design our own backend. The GCC project I have
downloaded is huge containing a lot of other
compilers, assemblers etc. Can you please guide me
where to find the gcc c compilers front end with
documentation. Please reply as soon as possible

thanks,
danish 

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