Foundations — Modules (C++20) — concept and syntax

5.2.32 · D1 · Coding › C++ Programming › Modules (C++20) — concept and syntax

Pehle aap parent note ki ek bhi line padh sako, aapke paas pehle se thodi ideas ka dhera hona chahiye: source file kya hoti hai, compiling karta kya hai, macro kya hota hai, "ek naam visible hai" ka matlab kya hai. Parent note inhe quietly assume karta hai. Yeh page har ek ko ground up se banata hai, us order mein jisme yeh ek doosre pe depend karte hain.

1. Source file — text ka ek page

Figure dekho. Baayein ek text file hai. Compiler text run nahi kar sakta — pehle usse translate karna padta hai machine instructions mein. Woh translation hi agla idea hai.

2. Compiling — text ko ek machine part mein badalna

3. Translation unit — jo compiler actually chhabta hai

Figure mein, main.cpp file apne aap mein chhoti hai, lekin #include ke header text paste karne ke baad, translation unit phool jaati hai. Woh phoolna — same header text hundreds of TUs mein copy hona — problem #1 hai jo parent note list karta hai ("slow builds"). Yeh idea itna central hai ki iska apna vault note hai: Translation Units and Linkage.

4. Preprocessor aur #include — copy-paste machine

Kyunki #include paste hai, do files jo same header include karti hain unhe har declaration ki do copies milti hain — isliye purani duniya mein include guards chahiye the (doosra paste skip karne ki #ifndef trick). Modules is poori pareshani ko delete kar dete hain; yahi parent ki "No guards needed" row hai.

5. #define aur macros — leaky hissa

Modules macros ko import ke paar nahi le jaate. Woh ek akela fact hai isliye parent "Macros do not leak" pe jashn manata hai. Aapko pata hona chahiye ki macro kya hai tab dekhoge ki na-leakna ek jeet kyun hai.

6. Names, visibility, aur scope

Figure teen nested visibility rings dikhata hai. Yeh ring picture exactly wahi hai jiske baare mein parent ka sabse bada mistake callout hai: export aur public alag rings hain.

• public / private — ek inner ring: kaun se class members doosra code touch kar sakta hai.
• export — ek outer ring: kaun se file-level names module boundary cross karke importers tak jaate hain.

Ek export ki gayi class ka private member exported-as-a-class hai lekin phir bhi privately sealed hai — do independent rings, dono khulni chahiye aapko woh reach karne ke liye.

7. export aur import — naye keywords

export module Name; ke baad sab kuch named-module region hai, jahan #include forbidden hai — iske pehle quarantine zone ka wahi reason hai.

8. Yeh sab kyun — build-speed ka payoff

Prerequisite map

Har arrow kehta hai "daayein idea samajhne se pehle baayein idea chahiye." Saare raaste parent ko feed karte hain: Modules (C++20).

Equipment checklist

Khud test karo — jawab zor se bolo, phir reveal karo.