3 ms·

The main practical takeaway is to prefer iterators over pre-generated arrays. Also, TIL according to the C standard, 'main' is not a reserved identifier! (http

by nur0n 9y ago

The main practical takeaway is to prefer iterators over pre-generated arrays. Also, TIL according to the C standard, 'main' is not a reserved identifier! (https://stackoverflow.com/questions/34764796/why-does-declaring-main-as-an-array-compile https://stackoverflow.com/questions/34764796/why-does-declar...) If anyone can clarify: I assumed that the gcc read literals directly into their 'target' type, but it seems like some literals (such as '-1u') are read as signed integers first then typecasted to the the target type?

shakna 9y ago
> Also, TIL according to the C standard, 'main' is not a reserved identifier! (https://stackoverflow.com/questions/34764796/why-does-declar... https://stackoverflow.com/questions/34764796/why-does-declar...) That's not quite true. Main is not required to be defined in a freestanding environment, but in a hosted environment: > 5.1.2.2.1 Program startup > 1 > The function called at program startup is named > main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters: int main(void) { /* ... */ } > or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared): int main(int argc, char *argv[]) { /* ... */ } > or equivalent; 10) or in some other implementation-defined manner. main can take on differing types, but it then becomes undefined-behaviour, which allows the compiler to do whatever it wants. (5.1.2.2.1 Program startup, C11 Standard http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf)
derefr 9y ago
> according to the C standard, 'main' is not a reserved identifier! In fact, main() is just a convention of libc. You can have C without libc. (Such as when writing a kernel!) Now, attempting to link a standalone executable without a '_start' symbol, on the other hand...
- shakna 9y ago
  > In fact, main() is just a convention of libc. No, it's not just a convention. 'main' is defined as the execution entrypoint in at least the C11 [0], C90 [1] standards. Both have both these forms defined: int main(void) {} int main(int argc, char* argv[]) {} You don't have to follow that convention, but then it becomes implementation-defined behaviour. C without libc can still expect to have a main. One doesn't imply the other. It's just without a main, you also have to manually link to _start as well. [0] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
- prattmic 9y ago
  > Now, attempting to link a standalone executable without a '_start' symbol, on the other hand... GNU ld and gold both support --entry to change the entry point. Alternatively, you can specify it in your linker script. https://gist.github.com/prattmic/1f3618025aab52b0e90e88445b6fc7d4 https://gist.github.com/prattmic/1f3618025aab52b0e90e88445b6... $ gcc -nostdlib -ffreestanding -Wl,--entry=foobar -o main main.S $ ./main; echo $? 42

by nur0n 9y ago

shakna 9y ago

> Also, TIL according to the C standard, 'main' is not a reserved identifier! (https://stackoverflow.com/questions/34764796/why-does-declar... https://stackoverflow.com/questions/34764796/why-does-declar...) That's not quite true. Main is not required to be defined in a freestanding environment, but in a hosted environment: > 5.1.2.2.1 Program startup > 1 > The function called at program startup is named > main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters: int main(void) { /* ... */ } > or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared): int main(int argc, char *argv[]) { /* ... */ } > or equivalent; 10) or in some other implementation-defined manner. main can take on differing types, but it then becomes undefined-behaviour, which allows the compiler to do whatever it wants. (5.1.2.2.1 Program startup, C11 Standard http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf)

derefr 9y ago

> according to the C standard, 'main' is not a reserved identifier! In fact, main() is just a convention of libc. You can have C without libc. (Such as when writing a kernel!) Now, attempting to link a standalone executable without a '_start' symbol, on the other hand...

shakna 9y ago
> In fact, main() is just a convention of libc. No, it's not just a convention. 'main' is defined as the execution entrypoint in at least the C11 [0], C90 [1] standards. Both have both these forms defined: int main(void) {} int main(int argc, char* argv[]) {} You don't have to follow that convention, but then it becomes implementation-defined behaviour. C without libc can still expect to have a main. One doesn't imply the other. It's just without a main, you also have to manually link to _start as well. [0] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
prattmic 9y ago
> Now, attempting to link a standalone executable without a '_start' symbol, on the other hand... GNU ld and gold both support --entry to change the entry point. Alternatively, you can specify it in your linker script. https://gist.github.com/prattmic/1f3618025aab52b0e90e88445b6fc7d4 https://gist.github.com/prattmic/1f3618025aab52b0e90e88445b6... $ gcc -nostdlib -ffreestanding -Wl,--entry=foobar -o main main.S $ ./main; echo $? 42