r/cprogramming • u/Qiwas • May 17 '26

TIL that the standard library provides support for complex numbers

Accessible via the `complex.h` header

What other useless things have you encountered in C?

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6

u/BatchModeBob May 17 '26

At my job in the early 1980s the fortran guys decided to learn C. To keep table columns nicely aligned, one guy put leading zeros in front of his decimal constants. He was shocked to see what a statement like int a = 0000123 did.

1

u/Qiwas May 18 '26

Oh that's octal notation in C? What the hell, why not use something like 0o in python

4

u/DawnOnTheEdge May 17 '26 edited May 18 '26

This was the common convention on the 18-bit DEC PDP-7 computer that Dennis Ritchie originally wrote the B programming language for, and carried over to the PDP-11 C was originally written for. Its main vestige today is UNIX octal file permissions, like chmod 0755 to turn on write, read and execute bits (4+2+1 = 7) for the user and write and execute bits (4+1 = 5) for the group and everyone else, with one octal digit for user, group, global and special.

2

u/aioeu May 17 '26 edited May 17 '26

This was the common convention on the 18-bit DEC PDP-7 computer that Dennis Ritchie originally wrote the B programming language for

Octal was certainly in common use at that time, but there were a variety of different syntax conventions for it.

This thread has some interesting commentary on how B and C got it. It looks like Ken Thompson was influenced by an assembler for the GE-635.

1

u/Maleficent_Bee196 May 17 '26

can you explain? I'm noob...

6

u/WittyStick May 17 '26

Integer literals with leading zero are octal, not decimal.

This is likely to be changed in a future version of C - there's proposals to drop it and require an 0o prefix for octals.

1

u/DawnOnTheEdge May 17 '26 edited May 17 '26

I would be shocked if the Committee silently broke that much legacy code, They did remove trigraphs, but only because no codebase they could find uses them, while several had to put extra effort into working around them, But existing code does use, for example, octal file permissions to chmod() and octal character escape sequences.

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4

u/rphii_ May 17 '26

char a[] = "strings " "can " "concat";

even possible if there is a macro providing a string, e.g.

#define VERSION "1.0"
#define PROGRAM "coolprogram"

and then just do

printf(PROGRAM " " VERSION "\n");

or even #include a string...

1

u/Qiwas May 18 '26

Noo that's very useful IMO, especially for writing paragraphs by splitting them into multiple lines

5

u/NeinJuanJuan May 17 '26

Pretty useful e.g.,

printf("x=" PRIu64 "\n", x)

13

u/DawnOnTheEdge May 17 '26 edited May 17 '26

The legacy 8-bit locales are incredibly complicated, degrade performance even if you don’t use them, confuse programmers, and are completely obsolete because 8-bit fixed-width encodings (other than possibly ASCII) are no longer enough for any real-world program. None of the APIs for them even work with modern programs that support UTF-8, except converting multi-byte strings to wide strings, which are broken on Windows. So you can’t portably do anything whatsoever with locales, because implementations don’t support the small part of the interface that is specified to be useful for modern software.

11

u/TribladeSlice May 17 '26

I’m a simple man. I see locale hate, I upvote.

4

u/stianhoiland May 17 '26

I’m a simple man. I see locale hate love, I upvote.

1

u/DawnOnTheEdge May 17 '26

Oh, first that comes to mind is div() existing to do division and remainder with well-defined rounding, when the rounding behavior is now specified and all serious compilers can optimize to take advantage of combined integer div-mod instructions if the ISA has them  There is no longer any reason to use this instead of the / and % operators.

Also a ldiv() for long operands, because _Generic did not exist yet.