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。
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
假设是POSIX,捕获stdout的简单代码:
#include <sys/wait.h>
#include <unistd.h>
#include <string>
#include <vector>
std::string qx(const std::vector<std::string>& args) {
int stdout_fds[2];
pipe(stdout_fds);
int stderr_fds[2];
pipe(stderr_fds);
const pid_t pid = fork();
if (!pid) {
close(stdout_fds[0]);
dup2(stdout_fds[1], 1);
close(stdout_fds[1]);
close(stderr_fds[0]);
dup2(stderr_fds[1], 2);
close(stderr_fds[1]);
std::vector<char*> vc(args.size() + 1, 0);
for (size_t i = 0; i < args.size(); ++i) {
vc[i] = const_cast<char*>(args[i].c_str());
}
execvp(vc[0], &vc[0]);
exit(0);
}
close(stdout_fds[1]);
std::string out;
const int buf_size = 4096;
char buffer[buf_size];
do {
const ssize_t r = read(stdout_fds[0], buffer, buf_size);
if (r > 0) {
out.append(buffer, r);
}
} while (errno == EAGAIN || errno == EINTR);
close(stdout_fds[0]);
close(stderr_fds[1]);
close(stderr_fds[0]);
int r, status;
do {
r = waitpid(pid, &status, 0);
} while (r == -1 && errno == EINTR);
return out;
}
为获得更多功能,欢迎代码贡献:
https://github.com/ericcurtin/execxx
其他回答
假设是POSIX,捕获stdout的简单代码:
#include <sys/wait.h>
#include <unistd.h>
#include <string>
#include <vector>
std::string qx(const std::vector<std::string>& args) {
int stdout_fds[2];
pipe(stdout_fds);
int stderr_fds[2];
pipe(stderr_fds);
const pid_t pid = fork();
if (!pid) {
close(stdout_fds[0]);
dup2(stdout_fds[1], 1);
close(stdout_fds[1]);
close(stderr_fds[0]);
dup2(stderr_fds[1], 2);
close(stderr_fds[1]);
std::vector<char*> vc(args.size() + 1, 0);
for (size_t i = 0; i < args.size(); ++i) {
vc[i] = const_cast<char*>(args[i].c_str());
}
execvp(vc[0], &vc[0]);
exit(0);
}
close(stdout_fds[1]);
std::string out;
const int buf_size = 4096;
char buffer[buf_size];
do {
const ssize_t r = read(stdout_fds[0], buffer, buf_size);
if (r > 0) {
out.append(buffer, r);
}
} while (errno == EAGAIN || errno == EINTR);
close(stdout_fds[0]);
close(stderr_fds[1]);
close(stderr_fds[0]);
int r, status;
do {
r = waitpid(pid, &status, 0);
} while (r == -1 && errno == EINTR);
return out;
}
为获得更多功能,欢迎代码贡献:
https://github.com/ericcurtin/execxx
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。
我会使用popen() (++waqas)。
但有时你需要阅读和写作……
似乎没有人再用困难的方式做事了。
(假设是Unix/Linux/Mac环境,或者是带有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())*/
}
您还可能希望使用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);
}
请注意,您可以通过将输出重定向到文件,然后读取它来获得输出
在std::system的文档中有显示
你可以通过调用WEXITSTATUS宏来接收退出码。
int status = std::system("ls -l >test.txt"); // execute the UNIX command "ls -l >test.txt"
std::cout << std::ifstream("test.txt").rdbuf();
std::cout << "Exit code: " << WEXITSTATUS(status) << std::endl;