Sort a 2D character Array using sort() in C++

Question

I have a 2D character array (I don't want to use array of std::string). How can I sort the strings (char*) in ascending order according to the length of the string using std::sort()?

I have tried the following. But it doesn't work.

char names[100][30];

bool comp(const char* a, const char* b){
    return strlen(a)<strlen(b);
}

int main(){
    ...
    //I want to sort the first n strings 
    sort(names,names+n,comp); //n<=100
    ...
}

I have found these errors:

1>e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3128) : error C2075: '_Val' : array initialization needs curly braces
1>        e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3150) : see reference to function template instantiation 'void std::_Insertion_sort1<_BidIt,bool(__cdecl *)(const char *,const char *),char[30]>(_BidIt,_BidIt,_Pr,_Ty (*))' being compiled
1>        with
1>        [
1>            _BidIt=char (*)[30],
1>            _Pr=bool (__cdecl *)(const char *,const char *),
1>            _Ty=char [30]
1>        ]
1>        e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3270) : see reference to function template instantiation 'void std::_Insertion_sort<_RanIt,bool(__cdecl *)(const char *,const char *)>(_BidIt,_BidIt,_Pr)' being compiled
1>        with
1>        [
1>            _RanIt=char (*)[30],
1>            _BidIt=char (*)[30],
1>            _Pr=bool (__cdecl *)(const char *,const char *)
1>        ]
1>        e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3279) : see reference to function template instantiation 'void std::_Sort<char(*)[30],int,bool(__cdecl *)(const char *,const char *)>(_RanIt,_RanIt,_Diff,_Pr)' being compiled
1>        with
1>        [
1>            _RanIt=char (*)[30],
1>            _Diff=int,
1>            _Pr=bool (__cdecl *)(const char *,const char *)
1>        ]
1>        e:\projects visual studio2008\sample\sample\sorting.cpp(51) : see reference to function template instantiation 'void std::sort<char(*)[30],bool(__cdecl *)(const char *,const char *)>(_RanIt,_RanIt,_Pr)' being compiled
1>        with
1>        [
1>            _RanIt=char (*)[30],
1>            _Pr=bool (__cdecl *)(const char *,const char *)
1>        ]
1>e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3133) : error C2106: '=' : left operand must be l-value
1>e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3140) : error C2106: '=' : left operand must be l-value
1>e:\program files (x86) in e\microsoft visual studio 9.0\vc\include\algorithm(3141) : error C2106: '=' : left operand must be l-value
1>Build log was saved at "file://e:\projects visual studio2008\sample\sample\Debug\BuildLog.htm"
1>sample - 4 error(s), 3 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

If your data is in

char names[100][30];

then you cannot sort "the pointers" because that data structure has no pointers at all... just 100*30 = 3000 characters one after another. Therefore to do the sorting you will need to actually move around the 100 rows will all their content.

std::sort cannot be used directly because the data structure is an array of arrays, and arrays are in C++ second-class citizens (for example you cannot assign an array to another).