[英]fscanf read access segfault
I a successfully open a file that contains initial key-value pairs. 我成功打开了一个包含初始键值对的文件。 The code looks like this:
代码如下:
char key_tmp[30];
int value_tmp, status_index;
FILE *ZMU_Init_fd = NULL;
ZMU_Init_fd = fopen("zmu/zmu.cfg", "r");
if(ZMU_Init_fd == NULL)
{
printf("Could not open file");
strerror(errno);
}
printf("key tmp is %s, value tmp is %d\n", key_tmp, value_tmp);
fscanf(ZMU_Init_fd, "%s %s", key_tmp, (char *)value_tmp);
printf("key tmp is %s, value tmp is %d\n", key_tmp, value_tmp);
When I run i get: 当我跑步时,我得到:
key tmp is y? value tmp is 1
then it segfaults. 然后它出现段错误。 When I change access to "w" the code sets zmu.cfg file size to 0 and i get:
当我将访问权限更改为“ w”时,代码将zmu.cfg文件大小设置为0,我得到:
key tmp is y? value tmp is 1
key tmp is y? value tmp is 1
no segfault... Interestingly enough, once the file is 0 bytes I can change the access back to "r" it no longer segfaults and i get: 没有段错误...有趣的是,一旦文件为0字节,我就可以将访问权限改回“ r”,它不再出现段错误,我得到:
key tmp is y? value tmp is 1
key tmp is y? value tmp is 1
I believe this has something to do with the way fscanf works. 我相信这与fscanf的工作方式有关。 Does fscanf delete the line from the file when it scans?
fscanf扫描时是否从文件中删除该行? All I am trying to do is get a key-value pair from a text file.
我要做的就是从文本文件中获取键值对。 I dont think i can use fread because the keys dont always have the same size.
我不认为我可以使用fread,因为密钥并不总是具有相同的大小。 I do NOT want the file modified, any thoughts?
我不想修改文件,有什么想法吗?
zmu.cfg looks like this: zmu.cfg看起来像这样:
MessageNum= message50
MsgInitOne= 0x01
MsgInitTwo= 0x04
MsgInitThree= 0x01
MessageNum= message50
VarOne= 0x02
VarTwo= 0x01
MessageNum= message50
MsgValOne= 0x01
MsgValTwo= 0x04
MsgValThree= 0x02
You haven't initialized key_tmp
before using it here. 您尚未在此处使用
key_tmp
进行初始化。
printf("key tmp is %s, value tmp is %d\n", key_tmp, value_tmp);
You are passing the wrong argument to fscanf
. 您将错误的参数传递给
fscanf
。 Casting value_tmp
to char*
does not enable it to hold a string. 将
value_tmp
为char*
不能使其容纳字符串。
fscanf(ZMU_Init_fd, "%s %s", key_tmp, (char *)value_tmp);
If the file contains an integer, use: 如果文件包含整数,请使用:
fscanf(ZMU_Init_fd, "%s %d", key_tmp, &value_tmp);
If the file contains a string, make sure that value_tmp
is a string large enough to hold the data. 如果文件包含字符串,请确保
value_tmp
是足以容纳数据的字符串。
char value_temp[1000];
and then, use: 然后,使用:
fscanf(ZMU_Init_fd, "%s %s", key_tmp, value_tmp);
You experience undefined behavior on your first call to: 首次拨打以下电话时,您会遇到不确定的行为 :
printf("key tmp is %s, value tmp is %d\n", key_tmp, value_tmp);
Neither key_tmp
or value_tmp
are initialized to any value. key_tmp
或value_tmp
都不会初始化为任何值。 After you attempt to access the uninitialized values, all bets are off. 尝试访问未初始化的值后,所有投注均关闭。 Your code could give you some output, or it could segfault -- you are experiencing undefined behavior -- anything could happen.
您的代码可能会给您一些输出,也可能会出现段错误-您正在遇到未定义的行为 -可能会发生任何事情。
Further, if you are reading an int
in value_tmp
, your fscanf
format string should be: 此外,如果您正在读取
value_tmp
的int
, value_tmp
fscanf
格式字符串应为:
fscanf(ZMU_Init_fd, "%s %d", key_tmp, &value_tmp);
Yay! 好极了! I changed the last lines to this:
我将最后几行更改为:
fscanf(ZMU_Init_fd, "%s %s", key_tmp, key_tmp);
printf("key tmp is %s, value tmp is %d\n", key_tmp, value_tmp);
fscanf(ZMU_Init_fd, "%s %x", key_tmp, &key_tmp);
printf("key tmp is %s, value tmp is %d\n", key_tmp, value_tmp);
and I get: 我得到:
key tmp is message50 value tmp is 8388608
key tmp is MsgInitOne value tmp is 1
Thanks for looking at my code, didn't think i needed to pass the address of key_tmp to fscanf for %i since I did not have to for %s. 感谢您查看我的代码,我认为我不需要将key_tmp的地址传递给fscanf以获得%i,因为我不必传递%s。
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