cproj(3)

💖 cproj — project into Riemann Sphere 💖

okay bestie, so this is the cproj page from the Linux man-pages (that's the manual name, mwah) and we're gonna talk about cproj, cprojf, and cprojl — the trio that yeets your complex number onto a sphere. no cap. ✨

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🌸 LIBRARY 🌸

Math library, that's libm, and you link it with -lm. don't forget the flag, she's sensitive 💅

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🎀 SYNOPSIS 🎀

#include <complex.h>

double complex cproj(double complex z);
float complex cprojf(float complex z);
long double complex cprojl(long double complex z);

look at them. three sisters. one job. 🫶

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🦋 DESCRIPTION 🦋

okay so picture this: these functions take a point in the plane and project it onto the surface of a Riemann Sphere, which is the one-point compactification of the complex plane. iykyk. 🧚

• Every finite point z projects to z itself. yes really. she stays exactly where she is, main character energy, no glow-up needed 👑
• Every complex infinite value gets projected to a single infinite value, namely positive infinity on the real axis. so like, all the infinities walk into the function and only one comes out. iconic. 🎀

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✨ ATTRIBUTES ✨

for an explanation of the terms used in this section, go peek at attributes(7).

• Interface: cproj(), cprojf(), cprojl()
• Attribute: Thread safety
• Value: MT-Safe

translation: MT-Safe, so she's safe across threads, go forth and be parallel bestie 💜

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🌈 STANDARDS 🌈

C11, POSIX.1-2008. we're standards-compliant and gorgeous. periodt. ⭐

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💀 HISTORY 💀

• glibc 2.1.
• C99, POSIX.1-2001.

⚠️ okay now the tea: in glibc 2.11 and earlier, the implementation does something different — a stereographic projection onto a Riemann Sphere. so if you're time-travelling back to old glibc, expect drama. not the same girl. 😭

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👀 SEE ALSO 👀

• cabs(3)
• complex(7)

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and that's the whole page bestie, go project something onto a sphere, you got this 💖

this lil beauty lives in Linux man-pages 6.20, dated 2026-02-08, filed under cproj(3) — bye bye, drink water, love u 🫶🌸