我正在寻找一种方法来获取从C++程序中运行命令的输出.我已经看过使用system()函数,但这只会执行一个命令.这是我正在寻找的一个例子:
std::string result = system("./some_command");
我需要运行一个任意命令并获取其输出.我看过Boost.org,但我找不到任何可以满足我需要的东西.
1> waqas..：
#include
#include
#include
#include
#include
#include
std::string exec(const char* cmd) {
std::array buffer;
std::string result;
std::unique_ptr 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版本:
#include
#include
#include
#include
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;
}
替换popen和pclose用于_popen和_pcloseWindows.
请注意,这只会抓取_stdout_而不是_stderr_.
unique_ptr更适合这里,从不使用实际引用计数.
另请注意,`result + = buffer`中可能会发生异常,因此管道可能无法正常关闭.
@Yasky:正在执行的程序是`int main(){puts("ERROR"); }`.
The answer is good but it would be better if you replace 'char*cmd' with 'const char*cmd'
这仍然是C ++ 17的最佳实践吗？
为什么在循环中使用`while(!feof(...))`和`if`语句,当你所要做的只是`while(fgets(...)!= NULL)`？
`while(!feof())`总是错的,当你没有真正读行时,`fgets`同样错了.使用`fread`并检查返回值.
@Janis:`bad_alloc`.
2> Jonathan Wak..：
同时获取stdout和stderr(以及写入stdin,这里没有显示)很容易使用我的pstreams标头,它定义了iostream类,其工作方式如下popen:
#include
#include
#include
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';
// read child's stderr
while (std::getline(proc.err(), line))
std::cout << "stderr: " << line << '\n';
}
然而,好的图书馆,LGPL杀了它.没有人需要一些简单的小功能,如果它将在商业项目中,那么它将把这样的功能作为动态库链接起来.
我不同意.`popen`要求你使用C stdio API,我更喜欢iostreams API.`popen`要求你手动清理`FILE`句柄,pstreams自动完成.`popen`只接受一个`const char*`作为参数,需要注意避免shell注入攻击,pstreams允许你传递类似于`execv`的字符串向量,这更安全.`popen`只给你一个管道,pstreams告诉你孩子的PID允许你发送信号,例如,如果它被阻止或没有退出就杀死它.即使您只需要单向IO,所有这些都是有优势的.
@chiliNUT新的1.0.1版本使用Boost许可证.
但是pstreams是在GNU LGPL许可下发布的,这对商业用途有点限制.http://stackoverflow.com/questions/2145216/gnu-lesser-gpl-application-sell
@tach:您不需要将其链接为动态库.除了头文件之外什么都没有.要确认LGPL可以与仅标题库一起使用,请查看[特征库常见问题解答](http://eigen.tuxfamily.org/index.php?title=Licensing_FAQ&oldid=1117#So_what_does_the_LGPL_require_me_to_do.3F).请注意,这适用于LGPL2,因此LGPL3可能会有其他并发症.
是的我打算更改v1.0版本的许可证(可能是Boost许可证)
3> Mr.Ree..：
我会用popen() (++ waqas).
但有时你需要阅读和写作......
似乎没有人再以艰难的方式做事了.
(假设Unix/Linux/Mac环境,或者可能是带有POSIX兼容层的Windows ......)
enum PIPE_FILE_DESCRIPTERS
{
READ_FD = 0,
WRITE_FD = 1
};
enum CONSTANTS
{
BUFFER_SIZE = 100
};
int
main()
{
int parentToChild[2];
int childToParent[2];
pid_t pid;
string dataReadFromChild;
char buffer[BUFFER_SIZE + 1];
ssize_t readResult;
int status;
ASSERT_IS(0, pipe(parentToChild));
ASSERT_IS(0, pipe(childToParent));
switch (pid = fork())
{
case -1:
FAIL("Fork failed");
exit(-1);
case 0: /* Child */
ASSERT_NOT(-1, dup2(parentToChild[READ_FD], STDIN_FILENO));
ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDOUT_FILENO));
ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDERR_FILENO));
ASSERT_IS(0, close(parentToChild [WRITE_FD]));
ASSERT_IS(0, close(childToParent [READ_FD]));
/* file, arg0, arg1, arg2 */
execlp("ls", "ls", "-al", "--color");
FAIL("This line should never be reached!!!");
exit(-1);
default: /* Parent */
cout << "Child " << pid << " process running..." << endl;
ASSERT_IS(0, close(parentToChild [READ_FD]));
ASSERT_IS(0, close(childToParent [WRITE_FD]));
while (true)
{
switch (readResult = read(childToParent[READ_FD],
buffer, BUFFER_SIZE))
{
case 0: /* End-of-File, or non-blocking read. */
cout << "End of file reached..." << endl
<< "Data received was ("
<< dataReadFromChild.size() << "): " << endl
<< dataReadFromChild << endl;
ASSERT_IS(pid, waitpid(pid, & status, 0));
cout << endl
<< "Child exit staus is: " << WEXITSTATUS(status) << endl
<< endl;
exit(0);
case -1:
if ((errno == EINTR) || (errno == EAGAIN))
{
errno = 0;
break;
}
else
{
FAIL("read() failed");
exit(-1);
}
default:
dataReadFromChild . append(buffer, readResult);
break;
}
} /* while (true) */
} /* switch (pid = fork())*/
}
您也可能想要使用select()和非阻塞读取.
fd_set readfds;
struct timeval timeout;
timeout.tv_sec = 0; /* Seconds */
timeout.tv_usec = 1000; /* Microseconds */
FD_ZERO(&readfds);
FD_SET(childToParent[READ_FD], &readfds);
switch (select (1 + childToParent[READ_FD], &readfds, (fd_set*)NULL, (fd_set*)NULL, & timeout))
{
case 0: /* Timeout expired */
break;
case -1:
if ((errno == EINTR) || (errno == EAGAIN))
{
errno = 0;
break;
}
else
{
FAIL("Select() Failed");
exit(-1);
}
case 1: /* We have input */
readResult = read(childToParent[READ_FD], buffer, BUFFER_SIZE);
// However you want to handle it...
break;
default:
FAIL("How did we see input on more than one file descriptor?");
exit(-1);
}
...或者您可以使用现有的posix_spawnp函数
你的`execlp`调用有一个错误:传递的最后一个`arg`指针必须是`(char*)NULL`才能正确终止可变参数列表(参见`execlp(3)`以供参考).
4> TarmoPikaro..：
对于Windows,popen也可以工作,但它会打开一个控制台窗口 - 它会快速闪烁在UI应用程序上.如果你想成为一名专业人士,最好禁用这种"闪烁"(特别是如果最终用户可以取消它).
所以这是我自己的Windows版本:
(此代码部分重新组合在代码项目和MSDN示例中编写的想法)
#include
#include
//
// 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
阅读[CreateProcess function(Windows)](https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v = vs.85).aspx)后,我发现这样做真的很危险:*`此函数的Unicode版本CreateProcessW可以修改此字符串的内容.因此,此参数不能是只读内存的指针(例如const变量或文字字符串).如果此参数是常量字符串,则该函数可能会导致访问冲突.*因此,最好先将命令行复制到单独的缓冲区中,以防止调用者更改其原始输入.
5> paxdiablo..：
两种可能的方法:
我不认为它popen()是C++标准的一部分(它是来自内存的POSIX的一部分),但它可以在我使用的每个UNIX上使用(并且你似乎是因为你的命令而瞄准UNIX ./some_command).
如果没有popen(),则可以使用system("./some_command >/tmp/some_command.out");,然后使用普通的I/O函数来处理输出文件.
6> 小智..：
以下可能是可移植的解决方案。它遵循标准。
#include
#include
#include
#include
#include
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;
}
我在gcc上收到此警告：“警告：使用`tmpnam`是危险的，最好使用`mkstemp`”
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