has it occurred to anyone that a simple std::cout might print a value in hex format when it is supposed to format just a decimal(like an integer)?
for example, I have a line as :
std::cout << "_Agent [" << target << "] is still
among " << ((target->currWorker)->getEntities().size()) << " entities
of worker[" << target->currWorker << "]" << std::endl;
which would print :
_Agent [0x2c6d530] is still among 0x1 entities of worker[0x2c520f0]
Note:
1-the said out put is sometime decimal and some times hex
2- the behaviour is smae even if I change ((target->currWorker)->getEntities().size()) to (int)((target->currWorker)->getEntities().size())
any hints?
thanks
You probably have set std::cout to print hex in prior in the context of your code but forget to reset. For example:
std::cout<<std::hex<<12;
/*blah blah blah*/
std::cout<<12; //this will print in hex form still
so you have to do like the following
std::cout<<std::dec<<12;
to print in decimal form.
Try to find line like this std::cout << std::showbase << std::hex; some where in your code, which sets std::cout to print output in hexadecimal with 0x base indicator prefix.
To reset it to show decimal add this line std::cout<<std::dec before the current cout.
You can learn more about c++ io manipulators flags here
Related
My program want to print epoc time in C++
If I print with fprintf/printf command, i get the correct output
fprintf(stdout, "epoch time=%u\t", (unsigned)time(NULL));
printf("var epoch=%u\n",(unsigned)time(NULL));
Output--->1528573149
But When i print the epoc time using C++, the output it is printed in "hex" format
cout<<"epoch time ="<< (unsigned)time(0);
Output---->5b1c2cdd
Unable to figure, how decimal value is implicitly converted to hexadecimal value.
Shows up as decimal for me, but try this:
std::cout << std::dec << (unsigned)time(0);
Or you can set desired format flag:
std::cout.setf(std::ios_base::dec, std::ios_base::basefield);
The only way this:
cout<<"epoch time ="<< (unsigned)time(0);
could print in hexadecimal is if you've previously set std::cout to hexadecimal mode.
For example:
#include <ctime>
#include <iostream>
#include <iomanip>
int main() {
std::cout << " decimal epoch time = " << time(0) << "\n";
std::cout << std::hex;
std::cout << "hexadecimal epoch time = " << time(0) << "\n";
}
The output on my system is:
decimal epoch time = 1528663129
hexadecimal epoch time = 5b1d8c59
This is in my opinion the most annoying feature of C++ I/O: To print a single item with a non-default format, you have to change the state of the output stream, which affects all later output on that stream.
If you want to print a single data item in hexadecimal (which you've probably done earlier in your program), you can do something like:
std::cout << "x = " << std::hex << x << std::dec << "\n";
This sets the output format back to decimal -- regardless of what it was previously. There's probably a complicated way to restore it to whatever it was.
I want to print my data in pdb format which is a specific format of storing atomic coordinates so that they can be read by some standard molecular visualisation softwares.
Currently I am using a work around regular C++ and combining my std::cout with printf to get a desired formatted output like this,
std::cout << std::setw(6) << "ATOM" << std::setw(5) << "0" << " "
<< std::setw(4) << "C" << std::setw(12) << global_id
<< " ";
printf("%8.3f %8.3f %8.3f %6.2f %6.2f \n", pos[0], pos[1], pos[2], tt, ss );
where global_id is an integer.
So how can I eliminate this printf and write the entire statement just by using std::cout with specified precision before and after decimal point.
Any help will be greatly appreciated.
The mechanism you are looking for is setprecision() as described here: http://en.cppreference.com/w/cpp/io/manip/setprecision
In conjunction with setw():
http://en.cppreference.com/w/cpp/io/manip/setw
has it occurred to anyone that a simple std::cout might print a value in hex format when it is supposed to format just a decimal(like an integer)?
for example, I have a line as :
std::cout << "_Agent [" << target << "] is still
among " << ((target->currWorker)->getEntities().size()) << " entities
of worker[" << target->currWorker << "]" << std::endl;
which would print :
_Agent [0x2c6d530] is still among 0x1 entities of worker[0x2c520f0]
Note:
1-the said out put is sometime decimal and some times hex
2- the behaviour is smae even if I change ((target->currWorker)->getEntities().size()) to (int)((target->currWorker)->getEntities().size())
any hints?
thanks
You probably have set std::cout to print hex in prior in the context of your code but forget to reset. For example:
std::cout<<std::hex<<12;
/*blah blah blah*/
std::cout<<12; //this will print in hex form still
so you have to do like the following
std::cout<<std::dec<<12;
to print in decimal form.
Try to find line like this std::cout << std::showbase << std::hex; some where in your code, which sets std::cout to print output in hexadecimal with 0x base indicator prefix.
To reset it to show decimal add this line std::cout<<std::dec before the current cout.
You can learn more about c++ io manipulators flags here
This question comes from a bug that I got into recently. I was trying to save some integer values to file as hex. As an example, this is what I should do:
cout << std::hex << value << endl; // (1)
But by mistake, I use it as the following:
cout << std::ios::hex << value << endl; // (2)
The compiler does not complain but obviously the result is not correct. I was trying a couple more values randomly and it seems that (2) actually give partially correct result except that it append 800 as a prefix. I don't understand where the 800 is coming from and I don't see a good reference anywhere. Can anybody explain what's happening under the hood?
cout << std::hex << 255 << endl; // output: FF
cout << std::ios::hex << 255 << endl; // output: 800ff
cout << std::hex << 135 << endl; // output: 87
cout << std::ios::hex << 135 << endl; // output: 80087
cout << std::hex << 11 << endl; // output: b
cout << std::ios::hex << 11 << endl; // output: 800b
This is actually std::ios_base::hex. It's an implementation-defined bitmask. Internally, the stream has an integer called fmtflags where it stores the current state of the formatting.
In your implementation, hex is the flag 0x800. Other flags will indicate whether it's in scientific notation mode, whether boolalpha is on, etc. etc.
The std::hex function sets the std::ios_base::hex flag in fmtflags.
So your output is the integer value of this flag (in hex since you sent std::hex previously).
std::hex is a manipulator, i.e., it is a function with a specific signature:
std::ios_base& hex(std::ios_base& stream) {
stream.setf(std::ios_base::hex, std::ios_base::basefield);
return stream;
}
There are some special output operators defined for stream to process manipulators. For the version operating on references to std::ios_base there is (ignoring that the operator is actually a function template):
std::ostream& operator<< (std::ostream& out, std::ios_base&(*manip)(std::ios_base&));
When used with a stream, the manipulator function is being called and it sets a specific format flag, in this case std::ios_base::hex (which is how std::ios::hex is actually defined). Since std::ios_base::hex is a member of a group of flags (the others are std::ios_base::dec and std::ios_base::oct) setting it also needs to clear any potential other flag in the group. Thus, setf() is called with a mask (std::ios_base::basefield) to clear any of the other potentially set flags.
The format flags std::ios_base::fmtflags is a bitmask type. The value std::ios_base::hex is one of the values. When formatting it you'll get some number, most likely a power of 2 (however, it doesn't have to be a power of 2). The value you see is simply 0x800 (i.e. 2048) printed using hex notation: setting any of the formatting flags (other than the width()) is sticky, i.e., they remain until the flag is unset. If you want to see the value 2048 (for the implementation you are using) you'd use
std::cout << std::dec << std::ios_base::hex << "\n"; // 2048
std::cout << std::hex << std::ios_base::hex << "\n"; // 800
std::cout << std::showbase << std::ios_base::hex << "\n"; // 0x800
The last line sets the flag showbase which indicates the base of an integer value with a prefix:
no prefix => decimal
a leading 0x => hexadecimal
a leading 0 (but no x) => octal
std::hex is a special object that, when applied to a stream using operator<<,
sets the basefield of the stream str to hex as if by calling str.setf(std::ios_base::hex, std::ios_base::base field)
std::ios::hex (aka std::ios_base::hex) is the actual bitmask value that gets passed to the setf method. Its value is implementation defined, and it seems to be 0x800 in your case.
I am using Qt, and I have an unsigned char *bytePointer and want to print out a number-value of the current byte. Below is my code, which is meant to give the int-value and the hex-value of the continuous bytes that I receive from a machine attached to the computer:
int byteHex=0;
byteHex = (int)*bytePointer;
qDebug << "\n int: " //this is the main issue here.
<< *bytePointer;
std::cout << " (hex: "
<< std::hex
<< byteHex
<< ")\n";
}
This gives perfect results, and I get actual numbers, however this code is going into an API and I don't want to use Qt-only functions, such as qDebug. So when I try this:
int byteHex=0;
byteHex = (int)*bytePointer;
std::cout << "\n int: " //I changed qDebug to std::cout
<< *bytePointer;
std::cout << " (hex: "
<< std::hex
<< byteHex
<< ")\n";
}
The output does give the hex-values perfectly, however the int-values return symbols (like ☺, └, §, to list a few).
My question is: How do I get std::cout to give the same output as qDebug?
EDIT: for some reason the symbols only occur with a certain Qt setting. I have no idea why it happened but it's fixed now.
As others pointed out in comment, you change the outputting to hex, but you do not actually set it back here:
std::cout << " (hex: "
<< std::hex
<< byteHex
<< ")\n";
You will need to apply this afterwards:
std::cout << std::dec;
Standard output streams will output any character type as a character, not a numeric value. To output the numeric value, convert to a non-character integer type:
std::cout << int(*bytePointer);