获取最后一个字符发送到std :: cout [英] Getting last char sent to std::cout
问题描述
我需要在main()执行结束时检查最后一个字符是否发送到stdout(通过 std :: cout
) \\ n'
(或平台特定的行尾)。如何测试这个?可以安全地假设没有使用C风格io(如printf)。
I need at the end of main() execution to check if last char sent to stdout (through std::cout
) was '\n'
(or platform specific end-of-line). How to test for this? It is safe to assume that C style io (like printf) was not used.
程序是C ++的REPL。它评估C ++表达式(或语句)并在stdout上打印结果。
Program is REPL for C++. It evaluates C++ expressions (or statements) and prints results on stdout. It is desirable that output would be always terminated with single new-line.
推荐答案
这是由@Kevin给出的类似的答案。但我相信它更适合你的需要。而不是使用一些你的流代替cout - 你可以用你自己的std :: cout替换streambuf:
It is similar answer to this given by @Kevin. However I believe it is better for your needs. Instead of using some your stream in place of cout - you can replace streambuf from std::cout with your own:
int main() {
std::streambuf* cbuf = std::cout.rdbuf(); // back up cout's streambuf
std::cout.flush();
keep_last_char_outbuf keep_last_buf(cbuf);
std::cout.rdbuf(&keep_last_buf); // assign your streambuf to cout
std::cout << "ala ma kota\n";
char last_char = keep_last_buf.get_last_char();
if (last_char == '\r' || last_char == '\n')
std::cout << "\nLast char was newline: " << int(last_char) << "\n";
else
std::cout << "\nLast char: '" << last_char << "'\n";
std::cout << "ala ma kota";
last_char = keep_last_buf.get_last_char();
if (last_char == '\r' || last_char == '\n')
std::cout << "\nLast char was newline: " << int(last_char) << "\n";
else
std::cout << "\nLast char: '" << last_char << "'\n";
std::cout.rdbuf(cbuf); // restore cout's original streambuf
}
预期输出:
ala ma kota
Last char was newline: 10
ala ma kota
Last char: 'a'
写一个任务 class keep_last_char_outbuf
不是很容易,查找装饰器模式和 streambuf 界面。
A task to write such class keep_last_char_outbuf
is not very easy, Look for decorator pattern and streambuf interface.
如果你没有时间玩这个 - 看看我的建议 ideone链接
If you don't have time for playing with this - look at my proposal ideone link
class keep_last_char_outbuf : public std::streambuf {
public:
keep_last_char_outbuf(std::streambuf* buf) : buf(buf), last_char(traits_type::eof()) {
// no buffering, overflow on every char
setp(0, 0);
}
char get_last_char() const { return last_char; }
virtual int_type overflow(int_type c) {
buf->sputc(c);
last_char = c;
return c;
}
private:
std::streambuf* buf;
char last_char;
};
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