我正在寻找一种方法来获得命令的输出，当它从c++程序中运行时。我已经看到了使用system()函数，但它只会执行一个命令。以下是我正在寻找的一个例子:
std::string result = system("./some_command");
我需要运行任意命令并获得其输出。我在boost.org上找过了，但是我还没有找到任何能满足我需要的东西。
当前回答
下面可能是一个可移植的解决方案。它遵循标准。
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <sstream>
std::string ssystem (const char *command) {
char tmpname [L_tmpnam];
std::tmpnam ( tmpname );
std::string scommand = command;
std::string cmd = scommand + " >> " + tmpname;
std::system(cmd.c_str());
std::ifstream file(tmpname, std::ios::in | std::ios::binary );
std::string result;
if (file) {
while (!file.eof()) result.push_back(file.get())
;
file.close();
}
remove(tmpname);
return result;
}
// For Cygwin
int main(int argc, char *argv[])
{
std::string bash = "FILETWO=/cygdrive/c/*\nfor f in $FILETWO\ndo\necho \"$f\"\ndone ";
std::string in;
std::string s = ssystem(bash.c_str());
std::istringstream iss(s);
std::string line;
while (std::getline(iss, line))
{
std::cout << "LINE-> " + line + " length: " << line.length() << std::endl;
}
std::cin >> in;
return 0;
}
其他回答
两种可能的方法:
我不认为popen()是c++标准的一部分(从内存来看，它是POSIX的一部分)，但它在我使用过的每个UNIX上都可用(您似乎针对的是UNIX，因为您的命令是./some_command)。 在不存在popen()的情况下，您可以使用system("。/some_command >/tmp/some_command.out");，然后使用正常的I/O函数处理输出文件。
#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
std::string exec(const char* cmd) {
std::array<char, 128> buffer;
std::string result;
std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);
if (!pipe) {
throw std::runtime_error("popen() failed!");
}
while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
result += buffer.data();
}
return result;
}
Pre-C + + 11版:
#include <iostream>
#include <stdexcept>
#include <stdio.h>
#include <string>
std::string exec(const char* cmd) {
char buffer[128];
std::string result = "";
FILE* pipe = popen(cmd, "r");
if (!pipe) throw std::runtime_error("popen() failed!");
try {
while (fgets(buffer, sizeof buffer, pipe) != NULL) {
result += buffer;
}
} catch (...) {
pclose(pipe);
throw;
}
pclose(pipe);
return result;
}
对于Windows，用_popen和_pclose替换popen和pclose。
获得stdout和stderr(也写入stdin，这里没有显示)与我的pstreams头很容易，它定义了iostream类的工作方式像popen:
#include <pstream.h>
#include <string>
#include <iostream>
int main()
{
// run a process and create a streambuf that reads its stdout and stderr
redi::ipstream proc("./some_command", redi::pstreams::pstdout | redi::pstreams::pstderr);
std::string line;
// read child's stdout
while (std::getline(proc.out(), line))
std::cout << "stdout: " << line << '\n';
// if reading stdout stopped at EOF then reset the state:
if (proc.eof() && proc.fail())
proc.clear();
// read child's stderr
while (std::getline(proc.err(), line))
std::cout << "stderr: " << line << '\n';
}
对于Windows, popen也可以工作，但它会打开一个控制台窗口-它会在你的UI应用程序上快速闪烁。如果你想成为一个专业人士，最好禁用这种“闪烁”(特别是如果最终用户可以取消它)。
下面是我自己的Windows版本:
(此代码部分重组自代码项目和MSDN示例中编写的想法。)
#include <windows.h>
#include <atlstr.h>
//
// Execute a command and get the results. (Only standard output)
//
CStringA ExecCmd(
const wchar_t* cmd // [in] command to execute
)
{
CStringA strResult;
HANDLE hPipeRead, hPipeWrite;
SECURITY_ATTRIBUTES saAttr = {sizeof(SECURITY_ATTRIBUTES)};
saAttr.bInheritHandle = TRUE; // Pipe handles are inherited by child process.
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe to get results from child's stdout.
if (!CreatePipe(&hPipeRead, &hPipeWrite, &saAttr, 0))
return strResult;
STARTUPINFOW si = {sizeof(STARTUPINFOW)};
si.dwFlags = STARTF_USESHOWWINDOW | STARTF_USESTDHANDLES;
si.hStdOutput = hPipeWrite;
si.hStdError = hPipeWrite;
si.wShowWindow = SW_HIDE; // Prevents cmd window from flashing.
// Requires STARTF_USESHOWWINDOW in dwFlags.
PROCESS_INFORMATION pi = { 0 };
BOOL fSuccess = CreateProcessW(NULL, (LPWSTR)cmd, NULL, NULL, TRUE, CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi);
if (! fSuccess)
{
CloseHandle(hPipeWrite);
CloseHandle(hPipeRead);
return strResult;
}
bool bProcessEnded = false;
for (; !bProcessEnded ;)
{
// Give some timeslice (50 ms), so we won't waste 100% CPU.
bProcessEnded = WaitForSingleObject( pi.hProcess, 50) == WAIT_OBJECT_0;
// Even if process exited - we continue reading, if
// there is some data available over pipe.
for (;;)
{
char buf[1024];
DWORD dwRead = 0;
DWORD dwAvail = 0;
if (!::PeekNamedPipe(hPipeRead, NULL, 0, NULL, &dwAvail, NULL))
break;
if (!dwAvail) // No data available, return
break;
if (!::ReadFile(hPipeRead, buf, min(sizeof(buf) - 1, dwAvail), &dwRead, NULL) || !dwRead)
// Error, the child process might ended
break;
buf[dwRead] = 0;
strResult += buf;
}
} //for
CloseHandle(hPipeWrite);
CloseHandle(hPipeRead);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return strResult;
} //ExecCmd
下面可能是一个可移植的解决方案。它遵循标准。
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <sstream>
std::string ssystem (const char *command) {
char tmpname [L_tmpnam];
std::tmpnam ( tmpname );
std::string scommand = command;
std::string cmd = scommand + " >> " + tmpname;
std::system(cmd.c_str());
std::ifstream file(tmpname, std::ios::in | std::ios::binary );
std::string result;
if (file) {
while (!file.eof()) result.push_back(file.get())
;
file.close();
}
remove(tmpname);
return result;
}
// For Cygwin
int main(int argc, char *argv[])
{
std::string bash = "FILETWO=/cygdrive/c/*\nfor f in $FILETWO\ndo\necho \"$f\"\ndone ";
std::string in;
std::string s = ssystem(bash.c_str());
std::istringstream iss(s);
std::string line;
while (std::getline(iss, line))
{
std::cout << "LINE-> " + line + " length: " << line.length() << std::endl;
}
std::cin >> in;
return 0;
}
