Need help on printf function

Question

2.00/5 (1 vote)

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Hi,

I am not much familiar with C++ but I am trying to do few simple things: print all characters as hex in single line.

test function:

C#

void Test::Start(void)
{
    unsigned char rnd[14]={0xDE ,0x75 ,0x27 ,0xA0 ,0x72 ,0xAB ,0x83 ,0x72 ,0xF2 ,0x7D ,0x34 ,0x3C ,0xAC ,0x36};

    prn("random:",rnd,14);
    for (int i=0; i<(int)sizeof(desKey); i++)
      { desKey[i]=char (i+1); }
    prn("desKey:",desKey,14);
}

print function:

C#

void Test::prn(std::string txt, unsigned char *a, int nLen)
{
    int len = (int) sizeof(a);
    printf("\n%t  Length: 2%d (Hex 2%x)\n", txt ,nLen);
    for (int i=0;i<nLen;i++) //go through all elements
        std::cout<<' 0x'<<std::hex<<a[i];
    std::cout<<std::endl;
}

Output unfortunately does not print string and also does not print chars as hex values. Length printed incorrectly as well.

Posted 30-Dec-11 7:52am

Tomazas77

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Comments

Tomazas77 30-Dec-11 14:13pm

output still not right:
random: Length: 14 (Hex 2109560Ì203078u203078'203078á203078r203078½203078â20307
8r203078‗203078}2030784203078<203078¼2030786)

desKey: Length: 14 (Hex 203078☺203078☻203078♥203078♦203078♣203078♠2030782030720
3078 203078
203078♫)03078♀203078
Press any key to continue . . .

It shoud come like
random: Length: 14 (Hex DE 75 27 A0 72 AB ......)
desKey: Length: 14 (Hex 01 02 03 04 05 06 ......)

3 solutions

Solution 4

Hi Tomazas,

If you are using a C++11 compiler that supports lambda functions...such as Visual Studio 2010 then you can do this with only a few lines of code:

C++

unsigned char rnd[14]={0xDE ,0x75 ,0x27 ,0xA0 ,0x72 ,0xAB ,0x83 ,0x72 ,0xF2 ,0x7D ,0x34 ,0x3C ,0xAC ,0x36};
vector<unsigned char> v;
v.assign(rnd,rnd+_countof(rnd));
std::for_each(v.begin(), v.end(), [](unsigned char c){std::cout << hex << uppercase << (int)c;});

With an older C++ compiler you could use a functor:

C++

void print(unsigned char c)
{
	std::cout << hex << uppercase << (int)c;
}

unsigned char rnd[14]={0xDE ,0x75 ,0x27 ,0xA0 ,0x72 ,0xAB ,0x83 ,0x72 ,0xF2 ,0x7D ,0x34 ,0x3C ,0xAC ,0x36};
vector<unsigned char> v;
v.assign(rnd,rnd+_countof(rnd));
std::for_each(v.begin(), v.end(),print);

Posted 30-Dec-11 16:04pm

Randor

Updated 30-Dec-11 16:32pm

v4

Comments

[no name] 30-Dec-11 22:09pm

The codeproject javascript editor is really buggy... it was modifying my c++ code... had to fix it twice.

Sergey Alexandrovich Kryukov 30-Dec-11 22:44pm

Good to see a use of lambda in C++, my 5.
--SA

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Richard MacCutchan · Accepted Answer · 2011-12-30T08:31:00

Solution 2

Quite a few things to address here.

C++

void Test::prn(std::string txt, unsigned char *a, int nLen)
{
    int len = (int) sizeof(a);
    printf("\n%t  Length: 2%d (Hex 2%x)\n", txt ,nLen);
    for (int i=0;i        std::cout<<' 0x'<<std::hex<<a[i];
    std::cout<<std::endl;
}

Why have you defined a constant character pointer (txt) as std::string?
sizeof(a) will always be 4 (or 8 on a 64 bit system).
You forgot to include the parameter for the hex value in your printf() statement. In fact you seem to be getting confused between your parameter specifications and actual parameters. What is %t supposed to represent?
Why mix printf() and cout calls; use one or the other for consistency?

Posted 30-Dec-11 8:31am

Richard MacCutchan

Comments

JackDingler 30-Dec-11 14:51pm

Good catch on the sizeof(a) thing.

An alternative is:

unsigned char rnd = "\xDE\x75\x27\xA0\x72\xAB\x83\x72\xF2\x7D\x34\x3C\xAC\x36";

Then you can do a strlen(rnd) to get the length.

Richard MacCutchan 30-Dec-11 15:11pm

Rather pointless since the caller is passing the length as the third parameter.

JackDingler 30-Dec-11 15:29pm

Heh, my brain is used up from doing a long code merge....

Richard MacCutchan 30-Dec-11 15:39pm

You're lucky, I rarely have an excuse :(

Sergey Alexandrovich Kryukov 30-Dec-11 22:34pm

Sure, a 5.
--SA

Tomazas77 · Accepted Answer · 2011-12-30T08:58:00

Solution 3

This worked for me (good enough for testing):

C#

void Test::prn(std::string txt, unsigned char *a, int nLen)
{
    printf("\n%s  Length: %d \n", txt.c_str() ,nLen);
    for (int i=0;i<nLen;i++)
    {
        int v = (int) a[i];
        char temp[16];
        sprintf(temp,"%02X, ",v);
        std::cout<<' '<<temp;
    }
    std::cout<<")"<<std::endl;
}

Posted 30-Dec-11 8:58am

Tomazas77

Comments

Richard MacCutchan 30-Dec-11 15:50pm

Why use sprintf() when you can use cout directly? You are also converting a simple const char* to a std::string for no reason, but to add overhead to your code.