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Add support for line buffering

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This commit is contained in:
Victor Zverovich 2024-01-24 16:10:01 -08:00
parent 6f260455aa
commit 6435b169ec
2 changed files with 24 additions and 0 deletions
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9
include/fmt/format-inl.h
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@ -1517,6 +1517,12 @@ template <typename F> class apple_file : public file_base<F> {
this->file_->_p += size;
this->file_->_w -= size;
}
bool needs_flush() const {
if ((this->file_->_flags & 1) == 0) return false; // 1 is __SLBF.
return memchr(this->file_->_p + this->file_->_w, '\n',
to_unsigned(-this->file_->_w));
}
};
// A fallback FILE wrapper.
@ -1529,6 +1535,7 @@ template <typename F> class fallback_file : public file_base<F> {
using file_base<F>::file_base;
auto is_buffered() const -> bool { return false; }
auto needs_flush() const -> bool { return false; }
auto get_read_buffer() const -> span<const char> {
return {&next_, has_next_ ? 1u : 0u};
@ -1581,7 +1588,9 @@ class file_print_buffer : public buffer<char> {
}
~file_print_buffer() {
file_.advance_write_buffer(size());
bool flush = file_.needs_flush();
funlockfile(file_);
if (flush) fflush(file_);
}
};

15
test/format-test.cc
View File

@ -1752,6 +1752,21 @@ TEST(format_test, big_print) {
EXPECT_WRITE(stdout, big_print(), std::string(count, 'x'));
}
// Windows CRT implements _IOLBF incorrectly (full buffering).
#if FMT_USE_FCNTL && !defined(_WIN32)
TEST(format_test, line_buffering) {
auto pipe = fmt::pipe();
auto read_end = pipe.read_end.fdopen("r");
auto write_end = pipe.write_end.fdopen("w");
setvbuf(write_end.get(), nullptr, _IOLBF, 4096);
write_end.print("42\n");
int n = 0;
int result = fscanf(read_end.get(), "%d", &n);
(void)result;
EXPECT_EQ(n, 42);
}
#endif
TEST(format_test, variadic) {
EXPECT_EQ(fmt::format("{}c{}", "ab", 1), "abc1");
}