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本篇内容介绍了“PostgreSQL中的User subroutines有什么作用”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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Flex输入文件由四部分组成:
%{
Declarations
%}
Definitions
%%
Rules
%%
User subroutines在规则之后是自定义例程,在scan.l中定义的例程主要是对输入的SQL语句进行解析以及执行初始化和事后清理工作等.
/* LCOV_EXCL_STOP */
/*
* Arrange access to yyextra for subroutines of the main yylex() function.
* We expect each subroutine to have a yyscanner parameter. Rather than
* use the yyget_xxx functions, which might or might not get inlined by the
* compiler, we cheat just a bit and cast yyscanner to the right type.
* 为主yylex()函数提供yyextra的访问.
* 我们期望每一个子例程都有参数:yyscanner.
* 相对于使用yyget_xxx函数(可能或不可能被编译器内联),我们强制yyscanner为正确的类型.
*/
#undef yyextra
#define yyextra (((struct yyguts_t *) yyscanner)->yyextra_r)
/* Likewise for a couple of other things we need. */
//定义其他需要的东西:yylloc/yyleng
#undef yylloc
#define yylloc (((struct yyguts_t *) yyscanner)->yylloc_r)
#undef yyleng
#define yyleng (((struct yyguts_t *) yyscanner)->yyleng_r)
/*
* scanner_errposition
* Report a lexer or grammar error cursor position, if possible.
* scanner_errposition : 如可以,报告词法或语法错误位置
*
* This is expected to be used within an ereport() call. The return value
* is a dummy (always 0, in fact).
* 该例程在ereport()调用中使用.返回值是伪列(实际上通常为0).
*
* Note that this can only be used for messages emitted during raw parsing
* (essentially, scan.l and gram.y), since it requires the yyscanner struct
* to still be available.
* 注意,这只能用于在原始解析期间产生的消息(scan.l & gram.y),
* 因为需要yyscanner结构体仍然可用才行.
*/
int
scanner_errposition(int location, core_yyscan_t yyscanner)
{
int pos;
if (location < 0)
return 0; /* no-op if location is unknown */
/* Convert byte offset to character number */
pos = pg_mbstrlen_with_len(yyextra->scanbuf, location) + 1;
/* And pass it to the ereport mechanism */
return errposition(pos);
}
/*
* scanner_yyerror
* Report a lexer or grammar error.
* 报告词法或语法错误.
*
* The message's cursor position is whatever YYLLOC was last set to,
* ie, the start of the current token if called within yylex(), or the
* most recently lexed token if called from the grammar.
* This is OK for syntax error messages from the Bison parser, because Bison
* parsers report error as soon as the first unparsable token is reached.
* Beware of using yyerror for other purposes, as the cursor position might
* be misleading!
* 该消息游标的位置在于YYLLOC最后设置的地方,比如如果在yylex()中则是当前的token开始位置,
* 或者如果是grammer调用则为最近一次的词法token.
* 在Bison解析器中抛出语法错误是没有问题的,因为Bison及诶吸气在遇到第一个无法解析的token时就会报错.
* 注意:如果处于其他目的使用yyerror,这时候游标的位置可能会出现误导.
*/
void
scanner_yyerror(const char *message, core_yyscan_t yyscanner)
{
const char *loc = yyextra->scanbuf + *yylloc;
if (*loc == YY_END_OF_BUFFER_CHAR)
{
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
/* translator: %s is typically the translation of "syntax error" */
errmsg("%s at end of input", _(message)),
lexer_errposition()));
}
else
{
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
/* translator: first %s is typically the translation of "syntax error" */
errmsg("%s at or near \"%s\"", _(message), loc),
lexer_errposition()));
}
}
/*
* Called before any actual parsing is done
* 初始化扫描器,在实际解析完成前调用
*/
core_yyscan_t
scanner_init(const char *str,
core_yy_extra_type *yyext,
const ScanKeyword *keywords,
int num_keywords)
{
Size slen = strlen(str);
yyscan_t scanner;
if (yylex_init(&scanner) != 0)
elog(ERROR, "yylex_init() failed: %m");
core_yyset_extra(yyext, scanner);
yyext->keywords = keywords;
yyext->num_keywords = num_keywords;
yyext->backslash_quote = backslash_quote;
yyext->escape_string_warning = escape_string_warning;
yyext->standard_conforming_strings = standard_conforming_strings;
/*
* Make a scan buffer with special termination needed by flex.
*/
yyext->scanbuf = (char *) palloc(slen + 2);
yyext->scanbuflen = slen;
memcpy(yyext->scanbuf, str, slen);
yyext->scanbuf[slen] = yyext->scanbuf[slen + 1] = YY_END_OF_BUFFER_CHAR;
yy_scan_buffer(yyext->scanbuf, slen + 2, scanner);
/* initialize literal buffer to a reasonable but expansible size */
yyext->literalalloc = 1024;
yyext->literalbuf = (char *) palloc(yyext->literalalloc);
yyext->literallen = 0;
return scanner;
}
/*
* Called after parsing is done to clean up after scanner_init()
* 在解析完成后调用,用于在scanner_init()之后进行清理.
*/
void
scanner_finish(core_yyscan_t yyscanner)
{
/*
* We don't bother to call yylex_destroy(), because all it would do is
* pfree a small amount of control storage. It's cheaper to leak the
* storage until the parsing context is destroyed. The amount of space
* involved is usually negligible compared to the output parse tree
* anyway.
* 不需要调用yylex_destroy(),因为所有需要做的事情只是释放一小块控制内存而已.
* 在解析上下文被销毁前,保留这部分内存成本会更低.
* 无论如何,与输出解析树相比,所涉及到的空间大小通常可以忽略不计.
*
* We do bother to pfree the scanbuf and literal buffer, but only if they
* represent a nontrivial amount of space. The 8K cutoff is arbitrary.
* 需要使用pfree释放扫描缓存和字面值缓存,但前提是它们代表了一个不小的空间才需要.
* 8K这个数值其实是很随意的.
*/
if (yyextra->scanbuflen >= 8192)
pfree(yyextra->scanbuf);
if (yyextra->literalalloc >= 8192)
pfree(yyextra->literalbuf);
}
static void
addlit(char *ytext, int yleng, core_yyscan_t yyscanner)
{
/* enlarge buffer if needed */
//增大缓存
if ((yyextra->literallen + yleng) >= yyextra->literalalloc)
{
do
{
yyextra->literalalloc *= 2;
} while ((yyextra->literallen + yleng) >= yyextra->literalalloc);
yyextra->literalbuf = (char *) repalloc(yyextra->literalbuf,
yyextra->literalalloc);
}
/* append new data */
//追加新数据
memcpy(yyextra->literalbuf + yyextra->literallen, ytext, yleng);
yyextra->literallen += yleng;
}
static void
addlitchar(unsigned char ychar, core_yyscan_t yyscanner)
{
/* enlarge buffer if needed */
if ((yyextra->literallen + 1) >= yyextra->literalalloc)
{
yyextra->literalalloc *= 2;
yyextra->literalbuf = (char *) repalloc(yyextra->literalbuf,
yyextra->literalalloc);
}
/* append new data */
yyextra->literalbuf[yyextra->literallen] = ychar;
yyextra->literallen += 1;
}
/*
* Create a palloc'd copy of literalbuf, adding a trailing null.
* 创建字面值缓存的拷贝,在末尾增加null.
*/
static char *
litbufdup(core_yyscan_t yyscanner)
{
int llen = yyextra->literallen;
char *new;
new = palloc(llen + 1);
memcpy(new, yyextra->literalbuf, llen);
new[llen] = '\0';
return new;
}
static int
process_integer_literal(const char *token, YYSTYPE *lval)
{
//处理整型字面值
int val;
char *endptr;
errno = 0;
val = strtoint(token, &endptr, 10);
if (*endptr != '\0' || errno == ERANGE)
{
/* integer too large, treat it as a float */
lval->str = pstrdup(token);
return FCONST;
}
lval->ival = val;
return ICONST;
}
static unsigned int
hexval(unsigned char c)
{
//十六进制
if (c >= '0' && c <= '9')
return c - '0';
if (c >= 'a' && c <= 'f')
return c - 'a' + 0xA;
if (c >= 'A' && c <= 'F')
return c - 'A' + 0xA;
elog(ERROR, "invalid hexadecimal digit");
return 0; /* not reached */
}
static void
check_unicode_value(pg_wchar c, char *loc, core_yyscan_t yyscanner)
{
if (GetDatabaseEncoding() == PG_UTF8)
return;
if (c > 0x7F)
{
ADVANCE_YYLLOC(loc - yyextra->literalbuf + 3); /* 3 for U&" */
yyerror("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8");
}
}
static bool
is_utf16_surrogate_first(pg_wchar c)
{
return (c >= 0xD800 && c <= 0xDBFF);
}
static bool
is_utf16_surrogate_second(pg_wchar c)
{
return (c >= 0xDC00 && c <= 0xDFFF);
}
static pg_wchar
surrogate_pair_to_codepoint(pg_wchar first, pg_wchar second)
{
return ((first & 0x3FF) << 10) + 0x10000 + (second & 0x3FF);
}
static void
addunicode(pg_wchar c, core_yyscan_t yyscanner)
{
char buf[8];
if (c == 0 || c > 0x10FFFF)
yyerror("invalid Unicode escape value");
if (c > 0x7F)
{
if (GetDatabaseEncoding() != PG_UTF8)
yyerror("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8");
yyextra->saw_non_ascii = true;
}
unicode_to_utf8(c, (unsigned char *) buf);
addlit(buf, pg_mblen(buf), yyscanner);
}
/* is 'escape' acceptable as Unicode escape character (UESCAPE syntax) ? */
static bool
check_uescapechar(unsigned char escape)
{
if (isxdigit(escape)
|| escape == '+'
|| escape == '\''
|| escape == '"'
|| scanner_isspace(escape))
{
return false;
}
else
return true;
}
/* like litbufdup, but handle unicode escapes */
static char *
litbuf_udeescape(unsigned char escape, core_yyscan_t yyscanner)
{
char *new;
char *litbuf,
*in,
*out;
pg_wchar pair_first = 0;
/* Make literalbuf null-terminated to simplify the scanning loop */
litbuf = yyextra->literalbuf;
litbuf[yyextra->literallen] = '\0';
/*
* This relies on the subtle assumption that a UTF-8 expansion cannot be
* longer than its escaped representation.
*/
new = palloc(yyextra->literallen + 1);
in = litbuf;
out = new;
while (*in)
{
if (in[0] == escape)
{
if (in[1] == escape)
{
if (pair_first)
{
ADVANCE_YYLLOC(in - litbuf + 3); /* 3 for U&" */
yyerror("invalid Unicode surrogate pair");
}
*out++ = escape;
in += 2;
}
else if (isxdigit((unsigned char) in[1]) &&
isxdigit((unsigned char) in[2]) &&
isxdigit((unsigned char) in[3]) &&
isxdigit((unsigned char) in[4]))
{
pg_wchar unicode;
unicode = (hexval(in[1]) << 12) +
(hexval(in[2]) << 8) +
(hexval(in[3]) << 4) +
hexval(in[4]);
check_unicode_value(unicode, in, yyscanner);
if (pair_first)
{
if (is_utf16_surrogate_second(unicode))
{
unicode = surrogate_pair_to_codepoint(pair_first, unicode);
pair_first = 0;
}
else
{
ADVANCE_YYLLOC(in - litbuf + 3); /* 3 for U&" */
yyerror("invalid Unicode surrogate pair");
}
}
else if (is_utf16_surrogate_second(unicode))
yyerror("invalid Unicode surrogate pair");
if (is_utf16_surrogate_first(unicode))
pair_first = unicode;
else
{
unicode_to_utf8(unicode, (unsigned char *) out);
out += pg_mblen(out);
}
in += 5;
}
else if (in[1] == '+' &&
isxdigit((unsigned char) in[2]) &&
isxdigit((unsigned char) in[3]) &&
isxdigit((unsigned char) in[4]) &&
isxdigit((unsigned char) in[5]) &&
isxdigit((unsigned char) in[6]) &&
isxdigit((unsigned char) in[7]))
{
pg_wchar unicode;
unicode = (hexval(in[2]) << 20) +
(hexval(in[3]) << 16) +
(hexval(in[4]) << 12) +
(hexval(in[5]) << 8) +
(hexval(in[6]) << 4) +
hexval(in[7]);
check_unicode_value(unicode, in, yyscanner);
if (pair_first)
{
if (is_utf16_surrogate_second(unicode))
{
unicode = surrogate_pair_to_codepoint(pair_first, unicode);
pair_first = 0;
}
else
{
ADVANCE_YYLLOC(in - litbuf + 3); /* 3 for U&" */
yyerror("invalid Unicode surrogate pair");
}
}
else if (is_utf16_surrogate_second(unicode))
yyerror("invalid Unicode surrogate pair");
if (is_utf16_surrogate_first(unicode))
pair_first = unicode;
else
{
unicode_to_utf8(unicode, (unsigned char *) out);
out += pg_mblen(out);
}
in += 8;
}
else
{
ADVANCE_YYLLOC(in - litbuf + 3); /* 3 for U&" */
yyerror("invalid Unicode escape value");
}
}
else
{
if (pair_first)
{
ADVANCE_YYLLOC(in - litbuf + 3); /* 3 for U&" */
yyerror("invalid Unicode surrogate pair");
}
*out++ = *in++;
}
}
/* unfinished surrogate pair? */
if (pair_first)
{
ADVANCE_YYLLOC(in - litbuf + 3); /* 3 for U&" */
yyerror("invalid Unicode surrogate pair");
}
*out = '\0';
/*
* We could skip pg_verifymbstr if we didn't process any non-7-bit-ASCII
* codes; but it's probably not worth the trouble, since this isn't likely
* to be a performance-critical path.
*/
pg_verifymbstr(new, out - new, false);
return new;
}
static unsigned char
unescape_single_char(unsigned char c, core_yyscan_t yyscanner)
{
switch (c)
{
case 'b':
return '\b';
case 'f':
return '\f';
case 'n':
return '\n';
case 'r':
return '\r';
case 't':
return '\t';
default:
/* check for backslash followed by non-7-bit-ASCII */
if (c == '\0' || IS_HIGHBIT_SET(c))
yyextra->saw_non_ascii = true;
return c;
}
}
static void
check_string_escape_warning(unsigned char ychar, core_yyscan_t yyscanner)
{
if (ychar == '\'')
{
if (yyextra->warn_on_first_escape && yyextra->escape_string_warning)
ereport(WARNING,
(errcode(ERRCODE_NONSTANDARD_USE_OF_ESCAPE_CHARACTER),
errmsg("nonstandard use of \\' in a string literal"),
errhint("Use '' to write quotes in strings, or use the escape string syntax (E'...')."),
lexer_errposition()));
yyextra->warn_on_first_escape = false; /* warn only once per string */
}
else if (ychar == '\\')
{
if (yyextra->warn_on_first_escape && yyextra->escape_string_warning)
ereport(WARNING,
(errcode(ERRCODE_NONSTANDARD_USE_OF_ESCAPE_CHARACTER),
errmsg("nonstandard use of \\\\ in a string literal"),
errhint("Use the escape string syntax for backslashes, e.g., E'\\\\'."),
lexer_errposition()));
yyextra->warn_on_first_escape = false; /* warn only once per string */
}
else
check_escape_warning(yyscanner);
}
static void
check_escape_warning(core_yyscan_t yyscanner)
{
if (yyextra->warn_on_first_escape && yyextra->escape_string_warning)
ereport(WARNING,
(errcode(ERRCODE_NONSTANDARD_USE_OF_ESCAPE_CHARACTER),
errmsg("nonstandard use of escape in a string literal"),
errhint("Use the escape string syntax for escapes, e.g., E'\\r\\n'."),
lexer_errposition()));
yyextra->warn_on_first_escape = false; /* warn only once per string */
}
/*
* Interface functions to make flex use palloc() instead of malloc().
* It'd be better to make these static, but flex insists otherwise.
*/
void *
core_yyalloc(yy_size_t bytes, core_yyscan_t yyscanner)
{
return palloc(bytes);
}
void *
core_yyrealloc(void *ptr, yy_size_t bytes, core_yyscan_t yyscanner)
{
if (ptr)
return repalloc(ptr, bytes);
else
return palloc(bytes);
}
void
core_yyfree(void *ptr, core_yyscan_t yyscanner)
{
if (ptr)
pfree(ptr);
}“PostgreSQL中的User subroutines有什么作用”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注创新互联网站，小编将为大家输出更多高质量的实用文章！
