The other likely size for it is that of int, being the “efficient” integer type for the platform. On architectures where it makes any difference whether the implementation chooses 1 or sizeof(int) there could be a trade-off between size (but if you’re happy to waste 7 bits per bool, why shouldn’t you be happy to …
#include <stdio.h> #include <sys/types.h> int main() { printf(“pid_t: %zu\n”, sizeof(pid_t)); printf(“uid_t: %zu\n”, sizeof(uid_t)); printf(“gid_t: %zu\n”, sizeof(gid_t)); } EDIT: Per popular request (and because, realistically, 99% of the people coming to this question are going to be running x86 or x86_64)… On an i686 and x86_64 (so, 32-bit and 64-bit) processor running Linux >= 3.0.0, the …
sizeof(array) is implemented entirely by the C compiler. By the time the program gets linked, what looks like a sizeof() call to you has been converted into a constant. Example: when you compile this C code: #include <stdlib.h> #include <stdio.h> int main(int argc, char** argv) { int a[33]; printf(“%d\n”, sizeof(a)); } you get .file “sz.c” …
There is no magic solution. C is not a reflective language. Objects don’t automatically know what they are. But you have many choices: Obviously, add a parameter Wrap the call in a macro and automatically add a parameter Use a more complex object. Define a structure which contains the dynamic array and also the size …
It just so happened that your class Base has 8 byte alignment requirement, but its last member has size 4. This leads to an empty padding area added at the end of Base‘s memory layout. That extra padding plays its role when you instantiate objects of class Base by themselves, as so called most-derived objects. …
From C99 spec, section 6.2.5, paragraph 27: A pointer to void shall have the same representation and alignment requirements as a pointer to a character type. Similarly, pointers to qualified or unqualified versions of compatible types shall have the same representation and alignment requirements. All pointers to structure types shall have the same representation and …
sizeof is not a function, it’s an operator. The parentheses are not part of the operator’s name. It’s failing because the value generated has the unsigned type size_t, which causes “the usual arithmetic conversions” in which -1 is converted to unsigned, in which case it’s a very large number. Basically you’re comparing 4 > 0xffffffffu, …
You cannot have an empty structure in C. It is a syntactic constraint violation. However gcc permits an empty structure in C as an extension. Furthermore the behaviour is undefined if the structure does not have any named member because C99 says : If the struct-declaration-list contains no named members, the behavior is undefined. So …
Bad choices on the part of the implementors? Seriously, according to the standard, “Plain ints have the natural size suggested by the architecture of the execution environment”, which does mean a 64 bit int on a 64 bit machine. One could easily argue that anything else is non-conformant. But in practice, the issues are more …
The [] is a flexible array member. They do not count towards the total size of the struct, because the C standard explicitly says so: 6.7.2.1/18 As a special case, the last element of a structure with more than one named member may have an incomplete array type; this is called a flexible array member. …