I was study in Hong Kong before the school changed its name, it is now known as the Hong Kong Chinese University. When I was in school, mandarin was call "国語" , no such thing as "普通话". and there was only traditional chinese, simplied chinese was unknown to all the chinese (it was not developed). In writting, both cantonese and mandarin was about the same. You may notice that all chinese books have no mandarin and/or cantonese version. It is to say that both cantonese and mandarin remain the same in writting. Note: Cantonese is a spoken dialect, it is not a language.

Basically the same. Cantonese is spoken and not usually written since it doesn't enjoy the status of the national language. Literate Cantonese speakers of older generations often used Classical Chinese, or now Mandarin-based Vernacular Chinese (or "standard Chinese"). Written Chinese spoken word for word in Cantonese sounds quite unnatural because Vernacular Chinese expressions are ungrammatical and unidiomatic in Cantonese. As a result, modern Cantonese speakers have developed their own written script, sometimes creating new characters for words that either do not exist or have been forgotten in standard Chinese. Cantonese characters Written Cantonese contains many characters not used in standard written Chinese in order to transcribe words not present in the standard lexicon. Despite attempts by the government of Hong Kong in the 1990s to standardize this character set, culminating in the release of the Hong Kong Supplementary Character Set for use in electronic communication, there is still significant disagreement about which characters are "correct" in written Cantonese. Synonyms Some characters used to represent words in Cantonese are synonyms of words used in standard written Chinese. For example, the character for "not" (不) is the synonym of 唔, the third-person pronoun (他 "he/she") is a synonym of 佢, the plural pronoun marker (們) is the synonym of 哋 and the possessive particle (的) is a synonym of 嘅. More details please see http://en.wikipedia.org/wiki/Written_Cantonese

广东使用的是粤语 听起来与普通话有差别 但是 书写格式和文字是一样的

Cantonese happens to be the Mother Tongue in Hong Kong, and has a solid written form, just like any other "national language", so there it enjoys much higher status than Mandarin. Mandarin has now become the second language for citizens of Hong Kong. There is technically only one set of Chinese characters. Although there are two kinds, traditional and simplified, they are parallel sets, so they are identical in meaning. Mandarin can be written in both traditional and simplified characters, as can Cantonese. A Mandarin speaker would have no trouble at all reading and comprehending Cantonese, and vice-versa, but speaking it would be a different matter altogether.

粤语当然是语言. 粤语词汇保留意很多古汉语词汇，很多词语与普通话相同，但意义不同. 况且,它自成一套完整书写系统,既能说也能写,名副其实"入得厨房,出得厅堂". 最喜欢粤语抵死诙谐创意十足兼具前人生活智慧的俗语.