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] = 0; i--) { if( !(str[i] >= '0' && str[i] = 'A' && 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 <strong style="color:transparent">来源gao@daima#com搞(%代@#码@网</strong>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.