In C++, strncpy() copies characters from one C-string into another, but it never writes more than count characters. If the source is shorter than count, the leftover bytes are filled with '\0'.
If the source is longer than count, dest does not get an ending '\0'. Add one yourself before you print it. All three arguments are required, and the two arrays must not overlap. Include <cstring>.
Use the third argument to limit how many characters are copied.
strncpy(dest, "Hello", 5);| Call | What it does |
|---|---|
strncpy(dest, "Hello", 5) | Copies at most 5 characters from Hello into dest. |
If the source is shorter than count, the rest of those bytes are filled with '\0'.
char* strncpy(char* destination, const char* source, size_t count);| Parameter | Description |
|---|---|
| dest | Required. The array you copy into. It must hold at least count characters. |
| source | Required. The characters you copy from. |
| count | Required. The most characters to write. |
| Return Value | Description |
|---|---|
| dest | The same pointer you passed in. |
strncpy()Copy a short greeting into a larger buffer.
#include <iostream>
#include <cstring>
int main() {
char dest[20];
const char* src = "Hello";
std::strncpy(dest, src, sizeof dest);
std::cout << dest << '\n';
return 0;
}count.'\0' from source is copied, then extra zeros pad to count.dest is safe because it is terminated.See that leftover slots become '\0'.
#include <iostream>
#include <cstring>
int main() {
char dest[6] = {'a', 'b', 'c', 'd', 'e', 'f'};
const char* src = "hi";
std::strncpy(dest, src, 5);
for (int i = 0; i < 6; ++i) {
if (dest[i] == '\0')
std::cout << "\\0 ";
else
std::cout << dest[i] << ' ';
}
std::cout << '\n';
return 0;
}h, i, then pads zeros up to 5 bytes.'f') was outside count, so it stays.strncpy behavior.When copying a long source into a small buffer, add '\0' yourself.
#include <iostream>
#include <cstring>
int main() {
char dest[6];
const char* src = "Hello World";
std::strncpy(dest, src, sizeof dest - 1);
dest[sizeof dest - 1] = '\0';
std::cout << dest << '\n';
return 0;
}dest[5] = '\0' so it is a valid C-string.Find the first character that matches any character in a set.
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