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POIs it dangerous to promote types in printf arguments?
 

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  1. POIs it dangerous to promote types in printf arguments?
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    <p>My questions stem from trying to use printf to log things when trying to build for multiple bit-depth platforms (32/64 for example).</p> <p>A problem that keeps rearing its ugly head is trying to print ints on multiple architectures. On 32 bit it would be something like</p> <pre><code>printf(" my int: %d\n", myInt); </code></pre> <p>but on 64 bit, it would have to be changed to </p> <pre><code>print (" my int: %ld\n", (long)myInt); </code></pre> <p>I have two related questions:</p> <ol> <li><p>My first thought was that when you tell printf to print a variable, giving it a format, it would look at the address of that variable and grab as many bytes as it needed for that format. This seemed like a big problem at first. For example if you had a variable myChar that was a char (1 byte), but used a format specifier of %d, that would tell printf to go to the address of myChar and grab the next 4 bytes to treat it like an int. If this were the case, it seems like printf would grab garbage date from neighboring variables (because it was grabbing 4 bytes, but the real value is only 1 byte). This appears to not be the case however. By using myChar and specifying %d, printf grabs 1 byte and then pads the upper 3 bytes with 0's. Is my understanding correct here?</p></li> <li><p>If the above is true, is there any real harm in always promoting variables up to their largest values to avoid the types of problems seen in the 32/64 bit case. For example if you have a short variable myShort, and an int variable, myInt, is there any downside in printing them always as:</p> <p>printf("myShort %ld", (long)myShort); printf("myInt %ld", (long)myInt);</p></li> </ol> <p>Thanks for any clarification.</p>
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    1. COpossible duplicate of [Automatic Type promotion in variadic function](http://stackoverflow.com/questions/7084857/automatic-type-promotion-in-variadic-function)
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    2. COIMO, not really that close to the dup question. I would encourage people to keep the discussion going here instead of voting to close.
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    3. COWhy do you believe that `printf("%d", myInt);` has to be changed for 64-bit platforms?
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