c++ - overloading operators for struct as map key -

hi i'm having problems overloading operator of struct use key. here struct intend use map key, has 2 char arrays:

struct fconfig {     char product[3];     char exchange[4];     bool operator < (const fconfig &rhs) const     {         return (strcmp(product, rhs.product) < 0 ||                   strcmp(exchange, rhs.exchange <0));     } }; 

my comparison long 1 of product or exchange not equal rhs's, key considered unique. use , "invalid operator <" during runtime. i'm totally new @ creating keys, i'm still having trouble understanding logic when overwriting < operator. appreciate help, thanks!

your confusion how operator < should work pretty common. want this:

bool operator < (const fconfig &rhs) const {    int product_comparision = strcmp(product,rhs.product);    if (product_comparision<0) return true;    if (product_comparision>0) return false;    return strcmp(exchange,rhs.exchange)<0; } 

since product primary key, time consider secondary key if primary key values equal.