

We are going to store some tuples into our table, that will map each {\itshape name} to a {\itshape number}. The cost to access a given number from the name should be very small, even with many entries in our table. This is the initial data\+: 
\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{\textcolor{keyword}{struct }\_Phone\_Entry \{}
\DoxyCodeLine{     \textcolor{keyword}{const} \textcolor{keywordtype}{char} *name; \textcolor{comment}{// Full name.}}
\DoxyCodeLine{     \textcolor{keyword}{const} \textcolor{keywordtype}{char} *number; \textcolor{comment}{// Phone number.}}
\DoxyCodeLine{\};}
\DoxyCodeLine{}
\DoxyCodeLine{\textcolor{keyword}{typedef} \textcolor{keyword}{struct }\_Phone\_Entry Phone\_Entry;}
\DoxyCodeLine{}
\DoxyCodeLine{\textcolor{keyword}{static} Phone\_Entry \_start\_entries[] = \{}
\DoxyCodeLine{       \{ \textcolor{stringliteral}{"{}Wolfgang Amadeus Mozart"{}}, \textcolor{stringliteral}{"{}+01 23 456-\/78910"{}} \},}
\DoxyCodeLine{       \{ \textcolor{stringliteral}{"{}Ludwig van Beethoven"{}}, \textcolor{stringliteral}{"{}+12 34 567-\/89101"{}} \},}
\DoxyCodeLine{       \{ \textcolor{stringliteral}{"{}Richard Georg Strauss"{}}, \textcolor{stringliteral}{"{}+23 45 678-\/91012"{}} \},}
\DoxyCodeLine{       \{ \textcolor{stringliteral}{"{}Heitor Villa-\/Lobos"{}}, \textcolor{stringliteral}{"{}+34 56 789-\/10123"{}} \},}
\DoxyCodeLine{       \{ NULL, NULL \}}
\DoxyCodeLine{\}; \textcolor{comment}{// \_start\_entries}}

\end{DoxyCodeInclude}
 Before starting to play with the hash, let\textquotesingle{}s write a callback that will be used to free the elements from it. Since we are just storing strduped strings, we just need to free them\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{\textcolor{keyword}{static} \textcolor{keywordtype}{void}}
\DoxyCodeLine{\_phone\_entry\_free\_cb(\textcolor{keywordtype}{void} *data)}
\DoxyCodeLine{\{}
\DoxyCodeLine{   free(data);}
\DoxyCodeLine{\}}

\end{DoxyCodeInclude}
 We also need a callback to iterate over the elements of the list later, so we are defining it now\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{\textcolor{keyword}{static} \mbox{\hyperlink{group__Eina__Types__Group_ga3fe0caf72e93b1bab1ca8ee3ccf3f226}{Eina\_Bool}}}
\DoxyCodeLine{\_phone\_book\_foreach\_cb(\textcolor{keyword}{const} \mbox{\hyperlink{group__Eina__Hash__Group_ga9a89d7d3ee260d3a60572ebf651b07e0}{Eina\_Hash}} *phone\_book \mbox{\hyperlink{group__Eina__Types__Group_ga82d751be730f849719ca292f9558be87}{EINA\_UNUSED}}, \textcolor{keyword}{const} \textcolor{keywordtype}{void} *key,}
\DoxyCodeLine{                       \textcolor{keywordtype}{void} *data, \textcolor{keywordtype}{void} *fdata \mbox{\hyperlink{group__Eina__Types__Group_ga82d751be730f849719ca292f9558be87}{EINA\_UNUSED}})}
\DoxyCodeLine{\{}
\DoxyCodeLine{   \textcolor{keyword}{const} \textcolor{keywordtype}{char} *name = key;}
\DoxyCodeLine{   \textcolor{keyword}{const} \textcolor{keywordtype}{char} *number = data;}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}\%s: \%s\(\backslash\)n"{}}, name, number);}
\DoxyCodeLine{}
\DoxyCodeLine{   \textcolor{comment}{// Return EINA\_FALSE to stop this callback from being called}}
\DoxyCodeLine{   \textcolor{keywordflow}{return} \mbox{\hyperlink{group__Eina__Types__Group_ga05c12dacc8b4058994df842b41be85fc}{EINA\_TRUE}};}
\DoxyCodeLine{\}}

\end{DoxyCodeInclude}
 Now let\textquotesingle{}s create our \mbox{\hyperlink{group__Eina__Hash__Group_ga9a89d7d3ee260d3a60572ebf651b07e0}{Eina\+\_\+\+Hash}} using \mbox{\hyperlink{group__Eina__Hash__Group_gad7203e20b1496445cb819c7862171c87}{eina\+\_\+hash\+\_\+string\+\_\+superfast\+\_\+new}} \+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \mbox{\hyperlink{group__Eina__Main__Group_gafee4bfc0e509b6ffed6598edf6f4b3de}{eina\_init}}();}
\DoxyCodeLine{}
\DoxyCodeLine{   phone\_book = \mbox{\hyperlink{group__Eina__Hash__Group_gad7203e20b1496445cb819c7862171c87}{eina\_hash\_string\_superfast\_new}}(\_phone\_entry\_free\_cb);}

\end{DoxyCodeInclude}
 Now we add the keys and data to the hash using \mbox{\hyperlink{group__Eina__Hash__Group_gafe3bb7c1f5616b4e158f60322e133260}{eina\+\_\+hash\+\_\+add}} . This means that the key is copied inside the table, together with the pointer to the data (phone numbers).


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \textcolor{keywordflow}{for} (i = 0; \_start\_entries[i].name != NULL; i++)}
\DoxyCodeLine{     \{}
\DoxyCodeLine{        \mbox{\hyperlink{group__Eina__Hash__Group_gafe3bb7c1f5616b4e158f60322e133260}{eina\_hash\_add}}(phone\_book, \_start\_entries[i].name,}
\DoxyCodeLine{                      strdup(\_start\_entries[i].number));}
\DoxyCodeLine{     \}}

\end{DoxyCodeInclude}
 Some basic manipulations with the hash, like finding a value given a key, deleting an entry, modifying an entry are exemplified in the following lines. Notice that the \mbox{\hyperlink{group__Eina__Hash__Group_gaabf2f2af1d93f969591f2c5b7378c543}{eina\+\_\+hash\+\_\+modify}} function returns the old value stored in that entry, and it needs to be freed, while the \mbox{\hyperlink{group__Eina__Hash__Group_gad8a9ac3c61ead249a6927a12e9de871a}{eina\+\_\+hash\+\_\+del}} function already calls our free callback\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \textcolor{comment}{// Look for a specific entry and get its phone number}}
\DoxyCodeLine{   phone = \mbox{\hyperlink{group__Eina__Hash__Group_ga45703d00fbabffc86e6836ffe98a4c92}{eina\_hash\_find}}(phone\_book, entry\_name);}
\DoxyCodeLine{   \textcolor{keywordflow}{if} (phone)}
\DoxyCodeLine{     \{}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}Printing entry.\(\backslash\)n"{}});}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}Name: \%s\(\backslash\)n"{}}, entry\_name);}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}Number: \%s\(\backslash\)n\(\backslash\)n"{}}, phone);}
\DoxyCodeLine{     \}}
\DoxyCodeLine{}
\DoxyCodeLine{   \textcolor{comment}{// Delete this entry}}
\DoxyCodeLine{   r = \mbox{\hyperlink{group__Eina__Hash__Group_gad8a9ac3c61ead249a6927a12e9de871a}{eina\_hash\_del}}(phone\_book, entry\_name, NULL);}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}Hash entry successfully deleted? \%d\(\backslash\)n\(\backslash\)n"{}}, r);}
\DoxyCodeLine{}
\DoxyCodeLine{   \textcolor{comment}{// Modify the pointer data of an entry and free the old one}}
\DoxyCodeLine{   phone = \mbox{\hyperlink{group__Eina__Hash__Group_gaabf2f2af1d93f969591f2c5b7378c543}{eina\_hash\_modify}}(phone\_book, \textcolor{stringliteral}{"{}Richard Georg Strauss"{}},}
\DoxyCodeLine{                            strdup(\textcolor{stringliteral}{"{}+23 45 111-\/11111"{}}));}
\DoxyCodeLine{   free(phone);}

\end{DoxyCodeInclude}
 The \mbox{\hyperlink{group__Eina__Hash__Group_ga53fd5f171289d63c5d8532bb28434cb3}{eina\+\_\+hash\+\_\+set}} function can be used to set a key-\/value entry to the table if it doesn\textquotesingle{}t exist, or to modify an existent entry. It returns the old entry if it was already set, and NULL otherwise. But since it will return NULL on error too, we need to check if an error has occurred\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \textcolor{comment}{// Modify or add an entry to the hash with eina\_hash\_set}}
\DoxyCodeLine{   \textcolor{comment}{// Let's first add a new entry}}
\DoxyCodeLine{   phone = \mbox{\hyperlink{group__Eina__Hash__Group_ga53fd5f171289d63c5d8532bb28434cb3}{eina\_hash\_set}}(phone\_book, \textcolor{stringliteral}{"{}Raul Seixas"{}},}
\DoxyCodeLine{                         strdup(\textcolor{stringliteral}{"{}+55 01 234-\/56789"{}}));}
\DoxyCodeLine{   \textcolor{keywordflow}{if} (!phone)}
\DoxyCodeLine{     \{}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}No previous phone found for Raul Seixas. "{}});}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}Creating new entry.\(\backslash\)n"{}});}
\DoxyCodeLine{     \}}
\DoxyCodeLine{   \textcolor{keywordflow}{else}}
\DoxyCodeLine{     \{}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}Old phone for Raul Seixas was \%s\(\backslash\)n"{}}, phone);}
\DoxyCodeLine{        free(phone);}
\DoxyCodeLine{     \}}
\DoxyCodeLine{}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}\(\backslash\)n"{}});}

\end{DoxyCodeInclude}
 There are different ways of iterate over the entries of a hash. Here we show two of them\+: using \mbox{\hyperlink{group__Eina__Hash__Group_ga2c23f8425d3afcc61827ab67b46d7190}{eina\+\_\+hash\+\_\+foreach}} and \mbox{\hyperlink{group__Eina__Iterator__Group_ga15b975bb881d955249ce13d4ebc96948}{Eina\+\_\+\+Iterator}}.


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}List of phones:\(\backslash\)n"{}});}
\DoxyCodeLine{   \mbox{\hyperlink{group__Eina__Hash__Group_ga2c23f8425d3afcc61827ab67b46d7190}{eina\_hash\_foreach}}(phone\_book, \_phone\_book\_foreach\_cb, NULL);}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}\(\backslash\)n"{}});}
\DoxyCodeLine{}
\DoxyCodeLine{   \textcolor{comment}{// Now iterate using an iterator}}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}List of phones:\(\backslash\)n"{}});}
\DoxyCodeLine{   it = \mbox{\hyperlink{group__Eina__Hash__Group_gaf0e7e38ec02c4bcfca3c3c4dd13c6af9}{eina\_hash\_iterator\_tuple\_new}}(phone\_book);}
\DoxyCodeLine{   \textcolor{keywordflow}{while} (\mbox{\hyperlink{group__Eina__Iterator__Group_ga83346e93c32dbebc8fd66e4f278140c5}{eina\_iterator\_next}}(it, \&data))}
\DoxyCodeLine{     \{}
\DoxyCodeLine{        \mbox{\hyperlink{struct__Eina__Hash__Tuple}{Eina\_Hash\_Tuple}} *t = data;}
\DoxyCodeLine{        \textcolor{keyword}{const} \textcolor{keywordtype}{char} *name = t-\/>key;}
\DoxyCodeLine{        \textcolor{keyword}{const} \textcolor{keywordtype}{char} *number = t-\/>data;}
\DoxyCodeLine{        printf(\textcolor{stringliteral}{"{}\%s: \%s\(\backslash\)n"{}}, name, number);}
\DoxyCodeLine{     \}}
\DoxyCodeLine{   \mbox{\hyperlink{group__Eina__Iterator__Group_gaf9261991a4b05dc63e3401278a3281f8}{eina\_iterator\_free}}(it); \textcolor{comment}{// Always free the iterator after its use}}

\end{DoxyCodeInclude}
 It\textquotesingle{}s also possible to change the key for a specific entry, without having to remove the entry from the table and adding it again\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \mbox{\hyperlink{group__Eina__Hash__Group_gaa390160f31c235d91947281244e77628}{eina\_hash\_move}}(phone\_book, \textcolor{stringliteral}{"{}Raul Seixas"{}}, \textcolor{stringliteral}{"{}Alceu Valenca"{}});}

\end{DoxyCodeInclude}
 We can remove all the elements from the table without free the table itself\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \textcolor{comment}{// Empty the phone book, but don't destroy it}}
\DoxyCodeLine{   \mbox{\hyperlink{group__Eina__Hash__Group_gabe2ba51e5dbf6fd5f60628b8e8f00eaa}{eina\_hash\_free\_buckets}}(phone\_book);}
\DoxyCodeLine{   printf(\textcolor{stringliteral}{"{}There are \%d items in the hash.\(\backslash\)n\(\backslash\)n"{}},}
\DoxyCodeLine{          \mbox{\hyperlink{group__Eina__Hash__Group_ga9289542f6724083eab306e5bb3ab10b0}{eina\_hash\_population}}(phone\_book));}

\end{DoxyCodeInclude}
 Or free the the entire table with its content\+:


\begin{DoxyCodeInclude}{0}
\DoxyCodeLine{   \mbox{\hyperlink{group__Eina__Hash__Group_gadb6acb720ce267cc1cd4f51893539f59}{eina\_hash\_free}}(phone\_book);}

\end{DoxyCodeInclude}


The full code for this example can be seen here\+: \mbox{\hyperlink{eina_hash_01_c}{Hash table in action}} 