## nng_msg_insert

Prepend to message body.

### Synopsis

```c
#include <nng/nng.h>

int nng_msg_insert(nng_msg *msg, const void *val, size_t size);
int nng_msg_insert_u16(nng_msg *msg, uint16_t val16);
int nng_msg_insert_u32(nng_msg *msg, uint32_t val32);
int nng_msg_insert_u64(nng_msg *msg, uint64_t val64);
```

### Description

These functions prepend data to the front of the body of message _msg_, reallocating it if necessary.footnote:[These functions make use of space pre-allocated in front of the message body if available.
Thus, they can often avoid performing any reallocation.]

The `nng_msg_insert` function prepends _size_ bytes, copying them from _val_.
The remaining functions prepend the specified value (such as _val32_) in network-byte order (big-endian).


### Return Values

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

### Errors

[horizontal]
`NNG_ENOMEM`:: Insufficient free memory exists.

### See Also

xref:nng_msg_append.adoc[nng_msg_append],
xref:nng_msg_body.adoc[nng_msg_body],
xref:nng_msg_trim.adoc[nng_msg_trim],
xref:nng_msg_realloc.adoc[nng_msg_realloc]
