C语言实现进制转换函数的实例详解

CATALOG(pg_proc,1255) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81) BKI_SCHEMA_MACRO{ NameData proname; /* procedure name */ /* 函数名，sql 中 select 函数名(); */ Oid  pronamespace; /* OID of namespace containing this proc */  /* 模式OID */ Oid  proowner; /* procedure owner */ /* 用户OID */ Oid  prolang; /* OID of pg_language entry */ float4 procost; /* estimated execution cost */  /* 估计执行成本 */ float4 prorows; /* estimated # of rows out (if proretset) */ /* 结果行估计数 */ Oid  provariadic; /* element type of variadic array, or 0 */ regproc protransform; /* transforms calls to it during planning */ bool proisagg; /* is it an aggregate? */ /* 是否为聚集函数 */ bool proiswindow; /* is it a window function? */  /* 是否为窗口函数 */ bool prosecdef; /* security definer */  /* 函数是一个安全定义器，也就是一个“setuid"函数 */ bool proleakproof; /* is it a leak-proof function? */  /* 有无其他影响 */ bool proisstrict; /* strict with respect to NULLs? */ /* 遇到 NULL 值是否直接返回 NULL */ bool proretset; /* returns a set? */ /* 函数返回一个集合 */ char provolatile; /* see PROVOLATILE_ categories below */ int16 pronargs; /* number of arguments */ /* 参数个数 */ int16 pronargdefaults; /* number of arguments with defaults */ /* 默认参数的个数 */ Oid  prorettype; /* OID of result type */ /* 返回参数类型OID */ /* * variable-length fields start here, but we allow direct access to * proargtypes */ oidvector proargtypes; /* parameter types (excludes OUT params) */ /* 存放函数参数类型的数组 */#ifdef CATALOG_VARLEN Oid  proallargtypes[1]; /* all param types (NULL if IN only) */ char proargmodes[1]; /* parameter modes (NULL if IN only) */ text proargnames[1]; /* parameter names (NULL if no names) */ pg_node_tree proargdefaults;/* list of expression trees for argument     * defaults (NULL if none) */ Oid  protrftypes[1]; /* types for which to apply transforms */ text prosrc BKI_FORCE_NOT_NULL; /* procedure source text */ /* 函数处理器如何调用函数，实现函数的函数名 */ text probin;  /* secondary procedure info (can be NULL) */ text proconfig[1]; /* procedure-local GUC settings */ aclitem proacl[1]; /* access permissions */#endif} FormData_pg_proc;

/* myfunc */DATA(insert OID = 6663 ( x_to_dec PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 23 "25 23" _null_ _null_ _null_ _null_ _null_ x_to_dec _null_ _null_ _null_ ));DESCR("x_to_dec.");OID = 6663  /* OID 唯一，不能与其他定义 OID 重复 */x_to_dec  /* sql 中 select x_to_dec(); */2 0 23 "25 23"  /* 传递两个参数; 默认 0; 返回值类型 OID = 23; 参数1类型 OID = 25, 参数2类型 OID = 23 */x_to_dec  /* 自定义函数名 */

postgres=# select oid,typname from pg_type where typname = 'text' or typname = 'int4'; oid | typname -----+--------- 23 | int4 25 | text(2 rows)

Datum  /* Datum 类型是PG系统函数大量引用的类型，其定义为：typedef uintptr_c Datum */x_to_dec (PG_FUNCTION_ARGS)  /* 函数名; 参数 */{  /* 获取参数 */ text *arg1 = PG_GETARG_TEXT_P(0); int32 arg2 = PG_GETARG_INT32(1);  /** 实现功能 **/  /* 返回 */ PG_RETURN_INT32(sum);}

Datum x_to_dec (PG_FUNCTION_ARGS){ int n = 0, i = 0, sum = 0, t = 0; text *arg1 = PG_GETARG_TEXT_P(0); int32 arg2 = PG_GETARG_INT32(1); char *str = text_to_cstring(arg1); n = strlen(str); switch(arg2) { case 2:  for(i = n - 1; i >= 0; i--)  {  if((str[i] - '0') != 1 && (str[i] - '0') != 0)  {   ereport(ERROR,   (errcode(ERRCODE_INVALID_PARAMETER_VALUE),   errmsg("Please enter the correct binary number, such as '110011'.")));  }  sum += (str[i] - '0') * ((int)pow(2, n - 1 - i));  }  break; case 8:  for(i = n - 1; i >= 0; i--)  {  if(!(str[i] >= '0' && str[i] <= '7'))  {   ereport(ERROR,   (errcode(ERRCODE_INVALID_PARAMETER_VALUE),   errmsg("Please enter the correct octal number, for example '34567'.")));  }  sum += (str[i] - '0') * ((int)pow(8, n - 1 - i));  }  break; case 16:  for(i = n - 1; i >= 0; i--)  {  if( !(str[i] >= '0' && str[i] <= '9') )  {   if(str[i] >= 'A' && str[i] <= 'F')   {   // Uppercase to lowercase   str[i] = str[i] + 32;   } else if ( !(str[i] >= 'a' && str[i] <= 'f') ) {   ereport(ERROR,    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),    errmsg("Please enter the correct hexadecimal number, for example '9f'.")));   }  }  if(str[i] <= '9')  {   t = str[i] - '0';  } else {   t = str[i] - 'a' + 10;  }  sum = sum * 16 + t;  }  break; default:  ereport(ERROR,  (errcode(ERRCODE_INVALID_PARAMETER_VALUE),  errmsg("Out of range! The second parameter, please enter: 2, 4, 16."))); } PG_RETURN_INT32(sum);}

/* * text_to_cstring * * Create a palloc'd, null-terminated C string from a text value. * * We support being passed a compressed or toasted text value. * This is a bit bogus since such values shouldn't really be referred to as * "text *", but it seems useful for robustness. If we didn't handle that * case here, we'd need another routine that did, anyway. */char *text_to_cstring(const text *t){ /* must cast away the const, unfortunately */ text  *tunpacked = pg_detoast_datum_packed((struct varlena *) t); int  len = VARSIZE_ANY_EXHDR(tunpacked); char  *result; result = (char *) palloc(len + 1); memcpy(result, VARDATA_ANY(tunpacked), len); result[len] = '/0'; if (tunpacked != t) pfree(tunpacked); return result;}

postgres=# select x_to_dec('111',2); x_to_dec ----------    7(1 row)postgres=# select x_to_dec('aA',16); x_to_dec ----------   170(1 row)postgres=# select x_to_dec('aA',1);ERROR: Out of range! The second parameter, please enter: 2, 4, 16.