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]

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]

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