1.copy paste your code here and copy the output without the quotes

2.type sudo gedit /usr/share/geany/snippets.conf (or you can go to snippets.conf from the tools menu in geany)

3.under the language section which you want to change

4.aliasname=paste the op which you have copied and save it

5.open geany ,in tools -> reload configuration

6.you are done just type aliasname and then press tab, your snippet is pasted.

print(repr("""
struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
"""))

Like in the above case under c++ section in that conf file ,i would do as customhash=the op you copied