我在我的Ubuntu机器上运行了一个程序(实际上是valgrind),并将stdout和stderr重定向到不同的文件。我很惊讶地看到屏幕上出现一条短信 - 这怎么可能?我怎么能在C ++程序中自己做到这一点?
编辑:这是我使用的命令和输出:
$ valgrind ./myprogram > val.out 2> val.err
*** stack smashing detected ***: ./myprogram terminated
EDIT2:再玩一下,事实证明myprogram,而不是valgrind,正在打印消息,如下所示,它看起来像gcc stack粉碎检测代码正在打印到/ dev / tty < / p>
答案 0 :(得分:16)
它不是由valgrind编写的,而是glibc而你的./myprogram正在使用glibc:
#define _PATH_TTY "/dev/tty"
/* Open a descriptor for /dev/tty unless the user explicitly
requests errors on standard error. */
const char *on_2 = __libc_secure_getenv ("LIBC_FATAL_STDERR_");
if (on_2 == NULL || *on_2 == '\0')
fd = open_not_cancel_2 (_PATH_TTY, O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1)
fd = STDERR_FILENO;
...
written = WRITEV_FOR_FATAL (fd, iov, nlist, total);
以下是glibc的一些相关部分:
void
__attribute__ ((noreturn))
__stack_chk_fail (void)
{
__fortify_fail ("stack smashing detected");
}
void
__attribute__ ((noreturn))
__fortify_fail (msg)
const char *msg;
{
/* The loop is added only to keep gcc happy. */
while (1)
__libc_message (2, "*** %s ***: %s terminated\n",
msg, __libc_argv[0] ?: "<unknown>");
}
/* Abort with an error message. */
void
__libc_message (int do_abort, const char *fmt, ...)
{
va_list ap;
int fd = -1;
va_start (ap, fmt);
#ifdef FATAL_PREPARE
FATAL_PREPARE;
#endif
/* Open a descriptor for /dev/tty unless the user explicitly
requests errors on standard error. */
const char *on_2 = __libc_secure_getenv ("LIBC_FATAL_STDERR_");
if (on_2 == NULL || *on_2 == '\0')
fd = open_not_cancel_2 (_PATH_TTY, O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1)
fd = STDERR_FILENO;
...
written = WRITEV_FOR_FATAL (fd, iov, nlist, total);
答案 1 :(得分:3)
该消息很可能来自GCC的堆栈保护功能或glib本身。如果它来自GCC,则使用fail()
函数输出,该函数直接打开/dev/tty
:
fd = open (_PATH_TTY, O_WRONLY);
_PATH_TTY
并非真正标准,但/dev/tty
存在的SingleUnix actually demands。
答案 2 :(得分:2)
以下是一些示例代码,它完全符合要求(感谢先前的答案指向了正确的方向)。两者都是用g ++编译的,即使重定向stdout和stderr,它也会在屏幕上打印一条消息。
对于Linux(Ubuntu 14):
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
int main( int, char *[]) {
printf("This goes to stdout\n");
fprintf(stderr, "This goes to stderr\n");
int ttyfd = open("/dev/tty", O_RDWR);
const char *msg = "This goes to screen\n";
write(ttyfd, msg, strlen(msg));
}
对于Windows 7,使用MinGW:
#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <conio.h>
void writeConsole( const char *s) {
while( *s) {
putch(*(s++));
}
}
int main( int, char *[]) {
printf("This goes to stdout\n");
fprintf(stderr, "This goes to stderr\n");
writeConsole( "This goes to screen\n");
}