In C++, strerror() turns an error number into a short message you can print. You usually pass errno right after a library call fails.
The error number is required. The result is a pointer to text that the library owns, so do not free it or change it. Read errno before another call replaces it. Include <cstring> and <cerrno>.
Pass the error number. That is usually errno just after a call fails.
strerror(errno);| Call | What it does |
|---|---|
strerror(errno) | Returns a message for the current error number. |
char* strerror(int errnum);| Parameter | Description |
|---|---|
| errnum | Required. The error number, usually errno right after the call that failed. |
| Return Value | Description |
|---|---|
| Message | A pointer to text that describes the error. The library owns that text. |
Look up ENOENT without opening a file.
#include <iostream>
#include <cstring>
#include <cerrno>
int main() {
std::cout << strerror(ENOENT) << '\n';
return 0;
}ENOENT is a standard “missing file” code.strerror maps that number to text.Use errno set by a failing C I/O call.
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cerrno>
int main() {
FILE* fp = std::fopen("no_such_file.txt", "r");
if (fp == nullptr) {
std::cout << "Open failed: " << strerror(errno) << '\n';
return 1;
}
std::fclose(fp);
return 0;
}fopen fails and sets errno.nullptr immediately.strerror(errno) for a clear reason.std::stringKeep the text safe if you call strerror again later.
#include <iostream>
#include <string>
#include <cstring>
#include <cerrno>
int main() {
std::string msg = strerror(EINVAL);
std::cout << "Saved: " << msg << '\n';
std::cout << "Again: " << strerror(ENOENT) << '\n';
std::cout << "Still: " << msg << '\n';
return 0;
}std::string copies the characters.strerror call may reuse the library buffer.msg copy is unchanged.Count the characters in a null-terminated C-string.
8 people found this page helpful