In C++, strlen() counts the characters in a C-string. It starts at the first character and stops when it reaches the ending '\0'. That ending mark is not included in the count.
You pass one string. "Hello" returns 5, and an empty string "" returns 0. The string must already end with '\0', or the count can run past the array. Include <cstring>.
Pass the C-string you want to measure.
strlen("Hello");| Call | What it does |
|---|---|
strlen("Hello") | Counts the letters in Hello. The result is 5. |
size_t strlen(const char* str);| Parameter | Description |
|---|---|
| str | Required. The C-string to measure. It must end with '\0'. |
| Return Value | Description |
|---|---|
| Length | How many characters come before '\0'. |
| 0 | The string is empty, like "". |
strlen()Count the characters in a greeting.
#include <iostream>
#include <cstring>
int main() {
const char* text = "Hello";
std::cout << "Length: " << std::strlen(text) << '\n';
return 0;
}"Hello" has five letters.'\0' ends the string but is not counted.size_t.strlen vs sizeofArray storage includes the null terminator; strlen does not.
#include <iostream>
#include <cstring>
int main() {
char text[] = "Hello";
std::cout << "strlen: " << std::strlen(text) << '\n';
std::cout << "sizeof: " << sizeof text << '\n';
return 0;
}strlen counts visible characters: 5.sizeof text is the array size: 5 letters + '\0' = 6.std::string::size()Same idea with modern C++ strings.
#include <iostream>
#include <string>
int main() {
std::string text = "Hello";
std::cout << "size: " << text.size() << '\n';
return 0;
}size() returns the stored length.'\0' yourself.strlen for C-strings; prefer size() for std::string.Append at most n characters from one C-string onto another.
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