Constraint to array dimension in C language
- by Summer_More_More_Tea
int KMP( const char *original, int o_len, const char *substring, int s_len ){
if( o_len < s_len )
return -1;
int k = 0;
int cur = 1;
int fail[ s_len ];
fail[ k ] = -1;
while( cur < s_len ){
k = cur - 1;
do{
if( substring[ cur ] == substring[ k ] ){
fail[ cur ] = k;
break;
}else{
k = fail[ k ] + 1;
}
}while( k );
if( !k && ( substring[ cur ] != substring[ 0 ] ) ){
fail[ cur ] = -1;
}else if( !k ){
fail[ cur ] = 0;
}
cur++;
}
k = 0;
cur = 0;
while( ( k < s_len ) && ( cur < o_len ) ){
if( original[ cur ] == substring[ k ] ){
cur++;
k++;
}else{
if( k == 0 ){
cur++;
}else{
k = fail[ k - 1 ] + 1;
}
}
}
if( k == s_len )
return cur - k;
else
return -1;
}
This is a KMP algorithm I once coded. When I reviewed it this morning, I find it strange that an integer array is defined as int fail[ s_len ]. Does the specification requires dimesion of arrays compile-time constant? How can this code pass the compilation?
By the way, my gcc version is 4.4.1.
Thanks in advance!
