I try to figure out how to print a certain value in a driver. In my case it is a ULONG value. At https://www.osronline.com/showthread.cfm?link=187470, it states that one should use the %U format specifier. So, I have the following code (only the relevant parts):
ULONG value;
value = 5;
DbgPrint("The value is: %U", value);
Compiling and loading works fine. But the "DbgView" output is not what I expected as you can see below:
The value is U
I hope someone can help. Thanks in advance.
Best regards
That is wrong
Per https://learn.microsoft.com/en-us/cpp/c-runtime-library/format-specification-syntax-printf-and-wprintf-functions?view=vs-2017#type-field-characters
To format ULONG, please use:
%u, for decimal integer.
%x, for unsigned hexadecimal integer; uses "abcdef."
%X, for unsigned hexadecimal integer; uses "ABCDEF."
Related
I am working with FastCgi, trying to generate a dynamic html webpage.
I am able to get the QUERY_STRING easily enough, but I am having trouble trying to copy it into a char array.
If there is even a shorter way of just getting the value from QUERY_STRING, please advise because I am a little over my head.
char *queryString = getenv(ENV_VARS[7]);
char newDeviceName[64];
strncpy( newDeviceName, *queryString, sizeof(*queryString) -1);
printf("------- %c ------------", newDeviceName);
This compiles with only warnings, but once i try to load the webpage, the characters are some weird Chinese looking characters. -> �ፙ�
Thank you in advance.
EDIT: More of my code
const char *ENV_VARS[] = {
"DOCUMENT_ROOT",
"HTTP_COOKIE",
"HTTP_HOST",
"HTTP_REFERER",
"HTTP_USER_AGENT",
"HTTPS",
"PATH",
"QUERY_STRING",
"REMOTE_ADDR",
"REMOTE_HOST",
"REMOTE_PORT",
"REMOTE_USER",
"REQUEST_METHOD",
"REQUEST_URI",
"SCRIPT_FILENAME",
"SCRIPT_NAME",
"SERVER_ADMIN",
"SERVER_NAME",
"SERVER_PORT",
"SERVER_SOFTWARE"
};
int main(void)
{
char deviceName[]=ADAPTERNAME;
time_t t;
/* Intializes random number generator */
srand((unsigned) time(&t));
while (FCGI_Accept() >= 0) {
printf("Content-type: text/html \r\n\r\n");
printf("");
printf("<html>\n");
printf("<script src=\"/js/scripts.js\"></script>");
/* CODE CODE CODE */
printf("<p> hi </p>");
printf("<p> hi </p>");
char *queryString = getenv(ENV_VARS[7]);
char newDeviceName[64];
if (queryString == NULL)
printf("<p> +++++ERROR++++++ </p>");
else {
strcpy( newDeviceName, queryString);
newDeviceName[sizeof(newDeviceName) - 1] = 0;
printf("<p> ------- %s ------------ </p> ", newDeviceName);
}
SOLVED: Amateur mistake, for some reason none of my new edits went into effect until after i restart my lighttpd server.
Your program has undefined behavior. Read those warnings issued by the compiler. They're important.
Don't dereference the pointer when you're passing the string to strncpy(). When you do that, you're now passing a single char. That's converted to a pointer when it's given to strncpy() (which is where you probably get your warning, i.e. passing a char to a function that expects a char*).
You also can't get the size of an array that has decayed to a pointer using sizeof. You're just getting the size of the pointer (which is probably either 8 or 4 bytes depending on your system). Since you don't know the length of the string anyway, it might even be better to just use strcpy() instead of strncpy().
Here's what your code probably should look like:
char *queryString = getenv(ENV_VARS[7]);
char newDeviceName[64];
strcpy( newDeviceName, queryString);
printf("------- %s ------------", newDeviceName); /* use %s to print strings */
The length on your strncpy is wrong [too short], the second argument is wrong, and the format string is incorrect.
Try this:
strncpy( newDeviceName, queryString, sizeof(newDeviceName) - 1);
newDeviceName[sizeof(newDeviceName) - 1] = 0;
printf("------- %s ------------", newDeviceName);
In the call to strncpy, it expects a char * for the second argument, but you pass it a char.
Also, the size is not correct. *queryString is a char and has size 1. Using sizeof(queryString) is not correct either because it will return the size of a pointer. What you actually want is the size of the detination buffer.
In the printf call the %c format specifier expects a char but you pass it a char *. You should instead use %s which expects a char * pointing to a null terminated string.
So what you want to do is this:
strncpy( newDeviceName, queryString, sizeof(newDeviceName) -1);
newDeviceName[sizeof(newDeviceName) - 1] = 0;
printf("------- %s ------------", newDeviceName);
What you want is
strncpy(newDeviceName, queryString, sizeof(newDeviceName)-1);
newDeviceName[63] = '\0'; // Guarantee NUL terminator
printf("----- %s -----", newDeviceName);
So multiple problems:
*queryString just gets you the first character, which strncpy tries to treat as a pointer.
sizeof(*queryString) is the size of a char (i.e. 1)
%c prints a single character, not the string
I'm trying to store results taken from a MySQL query into an array of structs. I can't seem to get the types to work though, and I've found the MySQL documentation difficult to sort through.
My struct is:
struct login_session
{
char* user[10];
time_t time;
int length;
};
And the loop where I'm trying to get the data is:
while ( (row = mysql_fetch_row(res)) != NULL ) {
strcpy(records[cnt].user, &row[0]);
cnt++;
}
No matter what I try though I constantly get the error:
test.c:45: warning: passing argument 1 of ‘strcpy’ from incompatible pointer type
/usr/include/string.h:128: note: expected ‘char * __restrict__’ but argument is of type ‘char **’
test.c:45: warning: passing argument 2 of ‘strcpy’ from incompatible pointer type
/usr/include/string.h:128: note: expected ‘const char * __restrict__’ but argument is of type ‘MYSQL_ROW’
Any pointers?
Multiple problems, all related to pointers and arrays, I recommend you do some reading.
First, char * user[10] is defining an array of 10 char * values, not an array of char, which is was I suspect you want. The warning even says as much, strcpy() expects a char *, the user field on its own is seen as a char **.
Second, you're one & away from what you want in the second argument.
Copied from mysql.h header:
typedef char **MYSQL_ROW; /* return data as array of strings */
A MYSQL_ROW is an array of char arrays. Using [] does a dereference, so you dereference down to a char * which is what strcpy() takes, but then you take the address of it using &.
Your code should look more like this:
struct login_session
{
char user[10];
time_t time;
int length;
};
while ( (row = mysql_fetch_row(res)) != NULL ) {
strcpy(records[cnt].user, row[0]);
cnt++;
}
I don't know what guarantees you have about the data coming from mysql, but if you can't be absolutely sure that the rows are <= 10 characters long and null ('\0') terminated, you should use strncpy() to avoid any possibility of overflowing the user array.
I've made this small experimental program in Arduino to see how the functions lowByte() and highByte() work. What exactly are they supposed to return when passed a value?
On entering the character '9' in the serial monitor it prints the following:
9
0
218
255
How does that come? Also, the last 2 lines are being printed for all values inputted. Why is this happening?
int i=12;
void setup()
{
Serial.begin(9600);
}
void loop()
{
if(Serial.available())
{
i = Serial.read() - '0'; // conversion of character to number. eg, '9' becomes 9.
Serial.print(lowByte(i)); // send the low byte
Serial.print(highByte(i)); // send the high byte
}
}
If you have this data:
10101011 11001101 // original
// HighByte() get:
10101011
// LowByte() get:
11001101
An int is a 16-bit integer on Arduino. So you are reading the high and low part as a byte.
As the actual buffer is "9\n", that is why the second bit prints out 'funny' numbers due to subtracting the result with '0'.
Serial.print needs to be formatted to a byte output if that's what you want to see.
Try:
Serial.print(lowByte, BYTE)
In addition to Rafalenfs' answer, Should you provide a larger data type:
00000100 10101011 11001101 // original
// HighByte() will NOT return: 00000100, but will return:
10101011
// LowByte() will still return:
11001101
Highbyte() returns the second lowest bit (as specified by the documentation: https://www.arduino.cc/reference/en/language/functions/bits-and-bytes/highbyte/)
How can I display the date using the function "MessageBox"?
Here is a link for several different ways to get the date and time:
Date & Time
Copied from site above:
Definition (from windows):
typedef struct _SYSTEMTIME {
WORD wYear;
WORD wMonth;
WORD wDayOfWeek;
WORD wDay;
WORD wHour;
WORD wMinute;
WORD wSecond;
WORD wMilliseconds;
} SYSTEMTIME, *PSYSTEMTIME, *LPSYSTEMTIME;
Implementation:
SYSTEMTIME st;
GetSystemTime(&st);
// You format how you want
DateTime dateTime = DateTime::Now;
MessageBox::Show(dateTime.ToString());
Other ToXString() functions can be found here
For example like this (I assumed you asked about native Windows API):
// Get current time
SYSTEMTIME now;
GetLocalTime(&now);
// Format the date using the default user language
TCHAR buffer[1024];
GetDateFormat(
MAKELCID(LANG_USER_DEFAULT, SORT_DEFAULT),
0,
&now,
NULL,
buffer,
1024
);
// Show it in a message box
MessageBox(HWND_DESKTOP, buffer, _T("Today"), MB_OK);
It's also possible to ask GetDateFormat to calculate the buffer length required to store the output. To do that pass NULL and 0 as last two parameters:
int length = GetDateFormat(
MAKELCID(LANG_USER_DEFAULT, SORT_DEFAULT),
0,
&now,
NULL,
NULL,
0
);
I am using C MySQL API
int numr=mysql_num_rows(res);
It always returns zero, but in my table there are 4 rows are there. However, I am getting the correct fields count.
what is the problem? Am i doing anything wrong?
Just a guess:
If you use mysql_use_result(), mysql_num_rows() does not return the correct value until all the rows in the result set have been retrieved.
(from the mysql manual)
The only reason to receive a zero from mysql_num_rows(<variable_name>) is because the query did not return anything.
You haven't posted the query here that you run and then assign the result to your res variable so we can't check it.
But try running that exact query in your DB locally through whatever DB management software you use and see if you are able to achieve any results.
If the query is working fine, then it must be the way you're running the query in C, otherwise your query is broken.
Maybe post up a bit more of your code from C where you make the query and then run it.
Thanks
If you just want to count the number of rows in a table, say
SELECT COUNT(*) FROM table_name
You will get back a single column in a single row containing the answer.
I too have this problem. But I noticed that mysql.h defines mysql_num_rows() to return a "my_ulonglong". Also in the header file you will see that there is a type def for my_ulonglong. On my system size of a my_ulonglong is 8 bytes. When we try to print this out or cast this to an int we probably get the first four bytes which are zero. However I printed out the eight bytes at the address of my_ulonglong variable and it prints all zeros. So I think this function just doesn't work.
`my_ulonglong numOfRows;
MYSQL *resource;
MYSQL *connection;
mysql_query(connection,"SELECT * FROM channels");
resource = mysql_use_result(connection);
numChannels = mysql_num_rows(resource);
printf("Writing numChannels: %lu\n", numChannels); // returns 0
printf("Size of numChannels is %d.\n", sizeof(numChannels)); // returns 8
// however
unsigned char * tempChar;
tempChar = (unsigned char *) &numChannels;
for (i=0; i< (int) sizeof(numChannels); ++i) {
printf("%02x", (unsigned int) *tempChar++);
}
printf("\n");
// returned 0000000000000000 so I think its a bug.
//mysql.h typedef for my_ulonglong and function mysql_num_rows()
#ifndef _global_h
#if defined(NO_CLIENT_LONG_LONG)
typedef unsigned long my_ulonglong;
#elif defined (__WIN__)
typedef unsigned __int64 my_ulonglong;
#else
typedef unsigned long long my_ulonglong;
#endif
#endif
my_ulonglong STDCALL mysql_num_rows(MYSQL_RES *res);
`