在進(jìn)行 TAU G2 編程時經(jīng)常會遇到下面的錯誤信息：

*************************** ERROR **************************

Dereferencing of NULL pointer.

Pointer assigned new data area at address .

? 有必要詳細(xì)說明一下。

? 一般出現(xiàn)這個問題，都是在訪問一個類或結(jié)構(gòu)的變量時出現(xiàn)的，例如下面是程序的片段。

D_attach_detach_group_identity???D_attach_detach_group_identity_type;

Group_identity_downlink??????????Group_identity_downlink_type;

Group_identity_downlinks?????????Group_identity_downlinks_type;

CArray < Group_identity_downlink,? 63 > ?data;

D_attach_detach_group_identity_type.pdu_type = 10 ;

D_attach_detach_group_identity_type.group_identity_report = false ;

D_attach_detach_group_identity_type.group_identity_acknowlegement = true ;

D_attach_detach_group_identity_type.group_identity_attach_detach_mode = true ;

D_attach_detach_group_identity_type.O_Bit = true ;

D_attach_detach_group_identity_type.M_Bit = true ;

Group_identity_downlink_type.Is_gIADTI_Present = true ;

Group_identity_downlink_type.gIADTI? = ?detach;

Group_identity_downlink_type.group_id_attach_or_detach.group_id_detachment_downlink = 3 ;

Group_identity_downlink_type.Is_gIAT_Present = true ;

Group_identity_downlink_type.gIAT? = ?gssi;

Group_identity_downlink_type.group_id_address.group_short_subscriber_identity = 1 ;

D_attach_detach_group_identity_type.group_identity_downlinks.data[ 0 ] = Group_identity_downlink_type;

D_attach_detach_group_identity_type.group_identity_downlinks.NoOfRepeatedElements? = ? 1 ;

在這個程序中，訪問 D_attach_detach_group_identity_type 、 Group_identity_downlink_type 和 Group_identity_downlinks_type 這三個變量的成員時都會報告錯誤。雖然可以忽略這個錯誤繼續(xù)運(yùn)行，但是如果這個錯誤很多，卻是非常麻煩。為什么會出現(xiàn)這個錯誤呢 ?

? 最主要的原因是在 TAU G2 中，類或結(jié)構(gòu)體變量都是看作指針的，如果在 WATCH 窗口看這些變量，在訪問變量前，它們都是 null ，而在賦值之后會顯示變量的地址，這和 C 語言對指針變量的處理基本相同。所以在給這些變量第 1 次賦值的時候就會報告訪問空指針。如果想避免這個問題，就應(yīng)該在賦值前先使用new 關(guān)鍵詞分配空間。如：

CArray < Group_identity_downlink,? 63 > ?data;

D_attach_detach_group_identity_type? = ? new ?D_attach_detach_group_identity();

Group_identity_downlink_type? = ? new ?Group_identity_downlink();

D_attach_detach_group_identity_type.pdu_type = 10 ;

D_attach_detach_group_identity_type.group_identity_report = false ;

D_attach_detach_group_identity_type.group_identity_acknowlegement = true ;

D_attach_detach_group_identity_type.group_identity_attach_detach_mode = true ;

……

這樣就可以避免出現(xiàn)此類問題了。