MODBUS_RECEIVE_CONFI(3)

💖 NAME 💖

modbus_receive_confirmation — bestie, this one grabs a confirmation request for you ✨

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🌸 SYNOPSIS 🌸

int modbus_receive_confirmation(modbus_t *ctx, uint8_t *rsp);

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🎀 DESCRIPTION 🎀

okay so modbus_receive_confirmation() shall receive a request through the socket of your context ctx. literally that's its whole job 💅

ngl though — this function is a debugging girlie. you must use it for debugging purposes, because the response you receive isn't checked against the initial request. no vibe check, no cross-referencing, nothing. it just hands you whatever showed up 🙈

it can also be used to receive requests that the library itself doesn't handle — so if libmodbus is like "not my department," this is your girl 🫶

🦋 sizing things (the part that matters) 🦋

the maximum size of the response depends on the backend you're running, so pay attention bestie:

• in RTU, your rsp array must be MODBUS_RTU_MAX_ADU_LENGTH bytes
• in TCP, it must be MODBUS_TCP_MAX_ADU_LENGTH bytes

and if you want code that's compatible with both (main character energy, honestly), use the constant MODBUS_MAX_ADU_LENGTH — that's the maximum value across all libmodbus backends 👑

⚠️ take care to allocate enough memory to store responses, or your server will straight up crash. not the cute kind of dramatic. the actual kind. 💀

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⭐ RETURN VALUE ⭐

if it works, the function shall store the confirmation request in rsp and return the response length. slay 💖

plot twist though: the returned request length can be zero if the indication request is ignored (for example, a query for another slave in RTU mode — not your business, not your problem 🍓).

otherwise it shall return -1 and set errno. yes, the classic. 🙃

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🌈 EXAMPLE 🌈

uint8_t rsp[MODBUS_MAX_ADU_LENGTH];
rc = modbus_receive_confirmation(ctx, rsp);

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👑 SEE ALSO 👑

modbus_send_raw_request(3)

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💜 AUTHORS 💜

the libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com> 🫶

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and that's the whole page, bestie!! this manual page is serving libmodbus v3.1.6, dated 11/17/2025 — so you know it's fresh. go forth and receive those confirmations responsibly ✨💅