new page cstdlib/system.md

Author: K10-K10

reference/cstdlib/system.md

@@ -0,0 +1,52 @@
+# system
+* cstdlib[meta header]
+
+
+```cpp
+int system( const char* command );
+```
+## 概要
+
+
+ホスト環境のコマンド呼び出す。(e.g. /bin/sh, cmd.exe)
+
+
+Returns an implementation-defined value (usually the value that the invoked program returns).
+
+If command is a null pointer, checks if the host environment has a command processor and returns a nonzero value if and only if the command processor exists.
+
+Parameters
+command	-	character string identifying the command to be run in the command processor. If a null pointer is given, command processor is checked for existence
+Return value
+Implementation-defined value. If command is a null pointer, returns a nonzero value if and only if the command processor exists.
+
+Notes
+On POSIX systems, the return value can be decomposed using WEXITSTATUS and WSTOPSIG.
+
+The related POSIX function popen makes the output generated by command available to the caller.
+
+An explicit flush of std::cout is also necessary before a call to std::system, if the spawned process performs any screen I/O.
+
+## 例
+
+```cpp example
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+
+int main()
+{
+    std::system("ls -l");
+    std::cout << std::ifstream("test.txt").rdbuf();
+}
+```
+
+## 出力結果
+
+```
+total 16
+-rwxr-xr-x 1 2001 2000 8859 Sep 30 20:52 a.out
+-rw-rw-rw- 1 2001 2000  161 Sep 30 20:52 main.cpp
+-rw-r--r-- 1 2001 2000    0 Sep 30 20:52 test.txt
+```
+