This documentation is for version v1.3.0 of NNG, but the latest released version is v1.8.0. see the documentation for v1.8.0 for the most up-to-date information.


#include <nng/nng.h>

int nng_ctx_get(nng_ctx ctx, const char *opt, void *val, size_t *valszp);

int nng_ctx_get_bool(nng_ctx ctx, const char *opt, bool *bvalp);

int nng_ctx_get_int(nng_ctx ctx, const char *opt, int *ivalp);

int nng_ctx_get_ms(nng_ctx ctx, const char *opt, nng_duration *durp);

int nng_ctx_get_size(nng_ctx ctx, const char *opt, size_t *zp);

int nng_ctx_get_string(nng_ctx ctx, const char *opt, char **strp);

int nng_ctx_get_uint64(nng_ctx ctx, const char *opt, uint64_t *u64p);


The nng_ctx_get() functions are used to retrieve option values for the context ctx. The actual options that may be retrieved in this way vary. A number of them are documented in nng_options(5).

Context options are protocol specific. The details will be documented with the protocol.


In all of these forms, the option opt is retrieved from the context ctx. The forms vary based on the type of the option they take.

The details of the type, size, and semantics of the option will depend on the actual option, and will be documented with the option itself.


This function is untyped and can be used to retrieve the value of any option. The caller must store a pointer to a buffer to receive the value in val, and the size of the buffer shall be stored at the location referenced by valszp.

When the function returns, the actual size of the data copied (or that would have been copied if sufficient space were present) is stored at the location referenced by valszp. If the caller’s buffer is not large enough to hold the entire object, then the copy is truncated. Therefore the caller should check for truncation by verifying that the returned size in valszp does not exceed the original buffer size.

It is acceptable to pass NULL for val if the value in valszp is zero. This can be used to determine the size of the buffer needed to receive the object.

It may be easier to use one of the typed forms of this function.

This function is for options which take a Boolean (bool). The value will be stored at ivalp.


This function is for options which take an integer (int). The value will be stored at ivalp.


This function is used to retrieve time durations (such as timeouts), stored in durp as a number of milliseconds. (The special value NNG_DUR_INFINITE means an infinite amount of time, and the special value NNG_DUR_DEFAULT means a context-specific default.)


This function is used to retrieve a size into the pointer zp, typically for buffer sizes, message maximum sizes, and similar options.


This function is used to retrieve a string into strp. This string is created from the source using nng_strdup() and consequently must be freed by the caller using nng_strfree() when it is no longer needed.


This function is used to retrieve a 64-bit unsigned value into the value referenced by u64p. This is typically used for options related to identifiers, network numbers, and similar.


These functions return 0 on success, and non-zero otherwise.



Incorrect type for option.


Parameter s does not refer to an open socket.


Size of destination val too small for object.


Insufficient memory exists.


The option opt is not supported.


The option opt is write-only.