A character sequence consisting of count1 characters starting at data1 is compared to a character sequence consisting of count2 characters starting at data2 as follows. First, calculate the number of characters to compare, as if by size_type rlen = std::min(count1, count2). Then compare the sequences by calling Traits::compare(data1, data2, rlen). For standard strings this function performs character-by-character lexicographical comparison. If the result is zero (the character sequences are equal so far), then their sizes are compared as follows:
當s1和s2作比較：（翻一下文檔的解釋）
先取s1，s2的較短長度作爲比較長度，然後按該長度進行比較，若出現ASCII碼的差，直接返回，若沒有出現差，再判斷二者的size，size1>size2，則返回>0.