使用管道从 STDIN 读取分叉进程时出现问题

我正在尝试创建一个辅助类来执行系统命令并通过管道支持获得响应。对于我只需要获得响应(命令没有 STDIN 可以使用(的情况，它按预期工作，对于管道支持，我得到乱码 STDIN，我无法找出根本原因。

处理此机制的主要函数是(请忽略小错误检查问题(

最小工作示例

#include <vector>
#include <string>
#include <iostream>
#include <sstream>
#include <unistd.h>
#include <sys/prctl.h>
#include <sys/types.h>
#include <signal.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <stdarg.h>
struct exec_cmd_t {
exec_cmd_t(std::vector<std::string> args) : args(args), has_executed(false), cpid(-1) { }
exec_cmd_t(const exec_cmd_t &) = delete;
exec_cmd_t(exec_cmd_t &&) = delete;
exec_cmd_t & operator=(const exec_cmd_t &) = delete;
exec_cmd_t & operator=(exec_cmd_t &&) = delete;
std::string operator()();
std::string pipe_cmd(const std::string & input);
std::string pipe_cmd();
~exec_cmd_t();
private:
std::vector<std::string> args;
bool has_executed;
int cpid;
std::stringstream in_stream;
std::stringstream out_stream;
friend std::string operator | (exec_cmd_t & first, exec_cmd_t & second);
friend std::string operator | (exec_cmd_t && first, exec_cmd_t && second);
friend std::string operator | (std::string, exec_cmd_t & second);
friend std::string operator | (std::string, exec_cmd_t && second);
};
std::string exec_cmd_t::pipe_cmd(const std::string & input) {
this->has_executed = true;
const int read_end = 0;
const int write_end = 1;
int read_pipe[2];
int write_pipe[2];
if (pipe(read_pipe) < 0 || pipe(write_pipe) < 0) {
this->has_executed = false;
return std::string{};
}
this->in_stream << input;
std::string line;
while(getline(this->in_stream, line)) {
if (line.size() == 0) {
continue;
}
int wr_sz = write(write_pipe[write_end], line.c_str(), line.size());
if (wr_sz <= 0) {
break;
}
write(write_pipe[write_end], "n", 1);
}
close(write_pipe[write_end]);
this->cpid = fork();
if (this->cpid == 0) {
dup2(write_pipe[read_end], STDIN_FILENO);
dup2(read_pipe[write_end], STDOUT_FILENO);
close(read_pipe[read_end]);
close(write_pipe[write_end]);
close(read_pipe[write_end]);
close(write_pipe[read_end]);
prctl(PR_SET_PDEATHSIG, SIGTERM);
char * params[args.size()];
const char * image_path = args[0].c_str();
for(int i = 1; i < args.size(); i++) {
params[i-1] = const_cast<char *>(args[i].c_str());
}
params[args.size()] = nullptr;
execv(image_path, params);
exit(1);
}
close(read_pipe[write_end]);
close(write_pipe[read_end]);
char buff[256];
int rd_sz = -1;
int flags = fcntl(read_pipe[0], F_GETFL, 0);
fcntl(read_pipe[read_end], F_SETFL, flags | O_NONBLOCK);
int status = 0;
waitpid(this->cpid, &status, 0);
this->has_executed = false;
int error_code = 0;
while((rd_sz = read(read_pipe[read_end], buff, sizeof(buff))) > 0) {
buff[rd_sz] = '';
this->out_stream << std::string{buff};
}
close(read_pipe[read_end]);
return this->out_stream.str();
}

std::string exec_cmd_t::pipe_cmd() {
static std::string empty_str{};
return pipe_cmd(empty_str);
}
std::string exec_cmd_t::operator()() {
return pipe_cmd();
}
exec_cmd_t::~exec_cmd_t() {
if (this->has_executed) {
int status;
waitpid(this->cpid, &status, WNOHANG);
if (!WIFEXITED(status)) {
kill(this->cpid, SIGKILL);
waitpid(this->cpid, &status, 0);
}
}
}
std::string operator | (exec_cmd_t & first, exec_cmd_t & second) {
return second.pipe_cmd(first());
}
std::string operator | (exec_cmd_t && first, exec_cmd_t && second) {
return second.pipe_cmd(first());
}
std::string operator | (std::string output, exec_cmd_t & second) {
return second.pipe_cmd(output);
}
std::string operator | (std::string output, exec_cmd_t && second) {
return second.pipe_cmd(output);
}
int main() {
auto str = exec_cmd_t{ {"/bin/echo", "echo", "hellonworldnornnot"} } | exec_cmd_t{ {"/bin/grep", "grep", "world", "-"} };
std::cout << str << std::endl;
return 0;
}

给我

grep: =V: No such file or directory                                                                                                                                                   
(standard input):world 

似乎 grep 正在执行两次，一次失败，没有这样的文件或目录，另一次成功。任何建议都会非常有帮助：-(。 提前谢谢。