memccpy - cppreference.com (original) (raw)
| | | | | --------------------------------------------------------------------------------------------------------------------- | | ----------- | | void* memccpy( void* restrict dest, const void* restrict src, int c, size_t count ); | | (since C23) |
Copies bytes from the object pointed to by src to the object pointed to by dest, stopping after any of the next two conditions are satisfied:
- count bytes are copied
- the byte (unsigned char)c is found (and copied).
The src and dest objects are interpreted as arrays of unsigned char.
The behavior is undefined if any condition is met:
- access occurs beyond the end of the dest array;
- the objects overlap (which is a violation of the restrict contract)
- either dest or src is an invalid or null pointer
[edit] Parameters
| dest | - | pointer to the object to copy to |
|---|---|---|
| src | - | pointer to the object to copy from |
| c | - | terminating byte, converted to unsigned char at first |
| count | - | number of bytes to copy |
[edit] Return value
If the byte (unsigned char)c was found, memccpy returns a pointer to the next byte in dest after (unsigned char)c. Otherwise it returns a null pointer.
[edit] Notes
The function is identical to the POSIX memccpy.
memccpy(dest, src, 0, count) behaves similar to strncpy(dest, src, count), except that the former returns a pointer to the end of the buffer written, and does not zero-pad the destination array. Thus, memccpy is useful for efficiently concatenating multiple strings.
char bigString[1000]; char* end = bigString + sizeof bigString; char* p = memccpy(bigString, "John, ", '\0', sizeof bigString - 1); if (p) p = memccpy(p - 1, "Paul, ", '\0', end - p); if (p) p = memccpy(p - 1, "George, ", '\0', end - p); if (p) p = memccpy(p - 1, "Joel ", '\0', end - p); if (!p) end[-1] = '\0'; puts(bigString); // John, Paul, George, Joel
[edit] Example
#include <ctype.h>
#include <stdio.h>
#include <string.h>
int main(void)
{
const char src[] = "Stars: Altair, Sun, Vega.";
const char terminal[] = {':', ' ', ',', '.', '!'};
char dest[sizeof src];
const char alt = '@';
for (size_t i = 0; i != sizeof terminal; ++i)
{
void* to = memccpy(dest, src, terminal[i], sizeof dest);
printf("Terminal '%c' (%s):\t"", terminal[i], to ? "found" : "absent");
// if terminal character was not found - print the whole dest
to = to ? to : dest + sizeof dest;
for (char* from = dest; from != to; ++from)
putchar(isprint(*from) ? *from : alt);
puts(""");
}
puts("\n" "Separate star names from distances (ly):");
const char *star_distance[] = {
"Arcturus : 37", "Vega : 25", "Capella : 43", "Rigel : 860", "Procyon : 11"
};
char names_only[64];
char *first = names_only;
char *last = names_only + sizeof names_only;
for (size_t t = 0; t != (sizeof star_distance) / (sizeof star_distance[0]); ++t)
{
if (first)
first = memccpy(first, star_distance[t], ' ', last - first);
else
break;
}
if (first)
{
*first = '\0';
puts(names_only);
}
else
puts("Buffer is too small.");
}
Output:
Terminal ':' (found): "Stars:" Terminal ' ' (found): "Stars: " Terminal ',' (found): "Stars: Altair," Terminal '.' (found): "Stars: Altair, Sun, Vega." Terminal '!' (absent): "Stars: Altair, Sun, Vega.@" Separate star names from distances (ly): Arcturus Vega Capella Rigel Procyon