[英]Strange behaviour of gcc in Debian
char * stft (const char *fmt, ...) {
va_list items;
char *out;
int magic = 0; // <-- here magic?
va_start (items, fmt);
vsprintf (out, fmt, items);
va_end (items);
return out;
}
Use like: 使用方式如下:
char *str = stft ("%s-%s %s", a, b, c);
This is working solution? 这是可行的解决方案吗? if delete unused "magic" variable - I have Segmentation fault after return string.
如果删除未使用的“魔术”变量-返回字符串后出现分段错误。 What doing wrong?
怎么了?
$ gcc --version gcc (Debian 4.4.5-8) 4.4.5 $ gcc --version gcc(Debian 4.4.5-8)4.4.5
$ uname -a Linux deep-station (squeeze) 2.6.32-5-686 #1 SMP Fri May 10 08:33:48 UTC 2013 i686 GNU/Linux $ uname -a Linux深度站(挤压)2.6.32-5-686#1 SMP Fri May 10 08:33:48 UTC 2013 i686 GNU / Linux
You are trying to write to an uninitialized pointer out
. 您正在尝试写入未初始化的指针
out
。 That's why you crash. 这就是为什么你崩溃。 It is badly undefined behaviour.
这是非常不确定的行为。 The magic is coincidental;
魔术是巧合; it does not make the behaviour any better defined.
它不会使行为得到更好的定义。
It is probably best to use vsnprintf()
: 最好使用
vsnprintf()
:
char *out = malloc(256);
...
vsnprintf(out, 256, fmt, items);
...
return out;
Or something similar. 或类似的东西。
You can improve this. 您可以改善这一点。 For example:
例如:
char *stft(const char *fmt, ...)
{
va_list items;
va_start(items, fmt);
int length = vsnprintf(0, 0, fmt, items);
va_end(items);
char *out = malloc(length+1);
if (out != 0)
{
va_start(items, fmt);
vsnprintf(out, length+1, fmt, items);
va_end(items);
}
return out;
}
Make sure you free the allocated memory in the calling code. 确保在调用代码中释放分配的内存。
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