Search and replace on a string

[Manuel Ferrero <mferrero reer it>]

I need to search some text in a big string ansd replace it with some 
other text.
The big string is null terminated and so is the replacement text.
I read that I can find the wanted text with g_strstr_len, but I can't 
figure out how can I do the substitution once I found the text.
Can please someone help me?
Pseudo code or just a hint will be appreciated.
TIA
--
Regards,
Manuel Ferrero
R&D department

Reer SpA	
Tel.  +39 011 2482215
Fax. +39 011 859867

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