cast safe

[grahamo]

Hi,

i know I should use the new style casts and I intend to however I
would like to know how I go about this;

I have an unsigned char* that a 3rd party API returned to me. The API
reads text from a file and gives me that test as an unsigned char*.
For the sake of this example the text string is "100"

unsigned char* data = foo();

I need to get this into an unsigned int, which is what it ultimately
should be however I'm not sure of the best approach. I can cast it to
a char* and then use sprintf(result, "%d", arg) but I'm not sure if
thats the best approach.

What's the *correct* way to achieve it... in terms of code correctness
and "correct approach".

Thanks much for any info (as usual:)

GrahamO

[Victor Bazarov]

grahamo wrote:

i know I should use the new style casts and I intend to however I
would like to know how I go about this;

I have an unsigned char* that a 3rd party API returned to me. The API
reads text from a file and gives me that test as an unsigned char*.
For the sake of this example the text string is "100"

unsigned char* data = foo();

I need to get this into an unsigned int, which is what it ultimately
should be however I'm not sure of the best approach. I can cast it to
a char* and then use sprintf(result, "%d", arg) but I'm not sure if
thats the best approach.
It's definitely not the best approach because you probably need 'sscanf'
and not 'sprintf'.
What's the *correct* way to achieve it... in terms of code correctness
and "correct approach".

You can roll your own conversion routine that would take unsigned char*
instead of char*, but in most cases you may cast unsigned char* to char*
without any problem, and then use 'strtol'.

Victor

[Mike Wahler]

"grahamo" <gr************@hotmail.com> wrote in message
news:79*************************@posting.google.co m...

Hi,

i know I should use the new style casts and I intend to however I
would like to know how I go about this;

I have an unsigned char* that a 3rd party API returned to me. The API
reads text from a file and gives me that test as an unsigned char*.
For the sake of this example the text string is "100"

unsigned char* data = foo();

I need to get this into an unsigned int, which is what it ultimately
should be however I'm not sure of the best approach. I can cast it to
a char* and then use sprintf(result, "%d", arg) but I'm not sure if
thats the best approach.

What's the *correct* way to achieve it... in terms of code correctness
and "correct approach".

Thanks much for any info (as usual:)

There are many ways which are 'correct'. The 'best'
depends upon your needs. E.g.:

std::istringstream iss(static_cast<char>(foo()));
int i(0);
if(!(iss >> i))
std::cerr << "Cannot convert text to integer\n";
else
/* do your thing */

If I wanted more detailed control and error detection
for the conversion, I might do something like this:

std::string s(static_cast<char>(foo()));

long tmp(0);
tmp = strtol(s.c_str(), /* etc */ );
/* (look up 'strtol()' for the other */
/* parameters and how to use it) */

int i(0);

if(tmp >= std::numeric_limits<int>::min() &&
tmp <= std::numeric_limits<int>::max())
i = static_cast<int>(tmp);
else
std::cerr << "value out of range for int\n";

Also, if 'foo()'s return value can be NULL, you need to check for
that before using it.

-Mike