c99

Is it safe to assume that sizeof(double) will always be greater than or equal to sizeof(void*) ? To put this in some context, is the following portable? int x = 100; double tmp; union { double dbl; void* ptr; } conv; conv.ptr = (void*)&x; tmp = conv.dbl; conv.dbl = tmp; printf("%d\n", *((int*)conv.ptr)); It does work on the few machines that I've tested it on, but I can see this going horribly wrong if sizeof(void*) > sizeof(double) . On current systems yes. double is 64 bits on all current and future systems because they're aligned with IEEE arithmetic's double-precision. It's unlikely but

I have a buffer and I don't want the user to enter more characters than the buffer can hold (to avoid a buffer overrun). I am using scanf and have done like this: char buffer[30] = {'\0'}; scanf("%30s", buffer); However, I know I am protected if the user enters more than 30. However, if the user enters more than 30, will the buffer be null terminated? scanf() with a "%s" conversion specifier adds a terminating null character to the buffer. But , you're asking for 30 characters, which really means 31 and only have space for 30. You should use a maximum field width of 29. char buffer[30] = {'\0'

I use DLog macro in an ARC project, and I got the warning: Implicit declaration of function 'DLog' is invalid in C99 You can find DLog from http://iphoneincubator.com/blog/debugging/the-evolution-of-a-replacement-for-nslog How to fix this warning? I actually had this warning when calling Dlog without a capital L. I changed it into DLog and everything worked fine. But you seem to have it correct. Make sure your Prefix.pch file is included in 'Build Settings' -> 'Prefix Header' 来源： https://stackoverflow.com/questions/9799838/arc-warning-implicit-declaration-of-function-dlog-is-invalid-in-c99

The Effective Type rule in C99 and C11 provides that storage with no declared type may be written with any type and, that storing a value of a non-character type will set the Effective Type of the storage accordingly. Setting aside the fact that INT_MAX might be less than 123456789, would the following code's use of the Effective Type rule be strictly conforming? #include <stdlib.h> #include <stdio.h> /* Performs some calculations using using int, then float, then int. If both results are desired, do_test(intbuff, floatbuff, 1); For int only, do_test(intbuff, intbuff, 1); For float only, do

The C99 standard of the C programming language defines the _Bool data type as a macro for another data type (as the language isn't able to deal with a type safe boolean). Is the _Bool a macro for unsigned char , unsigned int or some other data type? _Bool is a separate integere type that according to the C Standard. _Bool is a keyword of the C language. 2 An object declared as type _Bool is large enough to store the values 0 and 1. _Bool is unsigned integer type. The type _Bool and the unsigned integer types that correspond to the standard signed integer types are the standard unsigned integer

C99 6.5/6 The effective type of an object for an access to its stored value is the declared type of the object, if any. 75) If a value is stored into an object having no declared type through an lvalue having a type that is not a character type, then the type of the lvalue becomes the effective type of the object for that access and for subsequent accesses that do not modify the stored value. If a value is copied into an object having no declared type using memcpy or memmove, or is copied as an array of character type, then the effective type of the modified object for that access and for