QRegular expression - c++

Question

I can't find a way to match the text before opening curly bracket (i.e. p) using regex and Qt. My input file reads :
solvers
{
p
{
solver PCG;
preconditioner DIC;
tolerance 1e-06;
relTol 0.05;
}
q
{
solver PCG;
relTol 0.03;
}
}
and corresponding code from .cpp is :
rule.pattern = QRegularExpression("\\b(\\w+)(?=[\\s+\n]?\\{)",
QRegularExpression::MultilineOption);
Is anyone with better knowledge of Qt and regex can explain to me a way to achieve that?
EDIT #1
Thanks for the reply and comment. Two things :
I mistype my input file had no ">" symbol so I edited it in the above completed input.
I was trying to match the "p" of p-block and the "q" of q-block. A more extended version of my input is now edited above.
I found \}\s*(\w+)(?=\s*\{) to matched the "q" q-block but does not work in the code.
It seems to struggle with the return to line between "p" and the bracket "{".
EDIT #2 : show the code
in highlighter.cpp
#include "highlighter.h"
Highlighter::Highlighter(QTextDocument *parent)
: QSyntaxHighlighter(parent)
{
HighlightingRule rule;
(...)
varFormat.setFontWeight(QFont::Bold);
varFormat.setForeground(Qt::darkMagenta);
rule.pattern = QRegularExpression("^\\s+(\\w+)\\s*$",QRegularExpression::MultilineOption);
rule.format = varFormat;
highlightingRules.append(rule);
(...) }
void Highlighter::highlightBlock(const QString &text)
{
foreach (const HighlightingRule &rule, highlightingRules) {
QRegularExpressionMatchIterator matchIterator = rule.pattern.globalMatch(text);
while (matchIterator.hasNext()) {
QRegularExpressionMatch match = matchIterator.next();
setFormat(match.capturedStart(), match.capturedLength(), rule.format);
}
}
setCurrentBlockState(0);
int startIndex = 0;
if (previousBlockState() != 1)
startIndex = text.indexOf(commentStartExpression);
while (startIndex >= 0) {
QRegularExpressionMatch match = commentEndExpression.match(text, startIndex);
int endIndex = match.capturedStart();
int commentLength = 0;
if (endIndex == -1) {
setCurrentBlockState(1);
commentLength = text.length() - startIndex;
} else {
commentLength = endIndex - startIndex
+ match.capturedLength();
}
setFormat(startIndex, commentLength, multiLineCommentFormat);
startIndex = text.indexOf(commentStartExpression, startIndex + commentLength);
}
}

Answer 1

Have a look at [\\s+\n]?, it matches 1 or 0 occurrences of any whitespace or + characters. But there are more than 1 whitespace betwee solvers and {.
Replacing (?=[\\s+\n]?\\{) with (?=\\s*{) will already fix the issue. But you may also use
QRegularExpression("^\\s*(\\w+)\\s*\\{", QRegularExpression::MultilineOption)
to match the
^ - start of a line
\\s* - 0+ whitespaces
(\\w+) - Group 1 (you can get it via match.captured(1)): one or more word chars
\\s* - 0+ whitespaces followed with
\{ - a literal {.
See the regex demo.

Answer 2

Because p is not after {, but is after }
You can go this way:
[\{\}]\s*(\w+)(?=\s*\{) see https://regex101.com/r/wA1vu2/3
Or this this one:
(?P<tagname>[^{}\s]*)(?P<postspace>\s*)(?P<json_item>\{[^{}]*\})
?P<tagname> name of the match
?P<json_item>\{[^{}]*\} - leaf level item
(?P<postspace>\s*) - space between leaf item and leaf name
(?P<tagname>[^{}\s]*) - leaf name
https://regex101.com/r/wA1vu2/1/