## nng_msg_header_insert

Prepend to message header.

### Synopsis

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

int nng_msg_header_insert(nng_msg *msg, const void *val, size_t size);
int nng_msg_header_insert_u16(nng_msg *msg, uint16_t val16);
int nng_msg_header_insert_u32(nng_msg *msg, uint32_t val32);
int nng_msg_header_insert_u64(nng_msg *msg, uint64_t val64);
```

### Description

These function prependsdata to the front of the headers of message _msg_, reallocating if necessary.

The `nng_msg_header_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_header.adoc[nng_msg_header],
xref:nng_msg_header_append.adoc[nng_msg_header_append],
xref:nng_msg_header_trim.adoc[nng_msg_header_trim],
xref:nng_msg_realloc.adoc[nng_msg_realloc],