I noticed that, when assigning a std::string_view (or a std::string) to a character-array containing control characters (e.g. '\001' [Start Of Heading]), then gdb will represent that string_view with octal-escape characters between the already existing control-characters and another specific character (in my case, '=').
Example:
#include <array>
#include <iostream>
#include <string>
#include <string_view>
int main(int argc, char *argv[])
{
const std::array<char, 32> myArr =
{ '8', '=', 'F', 'I', 'X', 'T', '.', '1', '.', '1',
'\001', '9', '=', '9', '0', '\001', '3', '5', '=', 'A' };
const std::string_view view(myArr.begin(), myArr.size());
const std::string str (myArr.begin(), myArr.size());
std::cout << "VIEW: " << view << std::endl;
std::cout << "STRING: " << str << std::endl;
return 0;
}
Compiled with g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, this outputs:
VIEW: 8=FIXT.1.19=9035=A
STRING: 8=FIXT.1.19=9035=A
Looking at both view and str in the gdb debugger, we see:
"8=FIXT.1.1\001\071=90\001\063\065=A", '\000' <repeats 11 times>
We can see that after the first occurrence of '\001' , all "key" values are octal-escaped.
Why is this the case?
When removing the control characters from the array, the "escaping-conversion" is not done. However, in a real-world example, the array must contain control characters.
I do want to note that this is not a problem since substring lookups still work perfectly fine.
I'm just curious to know why gdb gives us this representation.
Think of what would happen if the digits after the control character were not escaped when GDB prints them. It would look like this:
"8=FIXT.1.1\0019=90\00135=A", '\000' <repeats 11 times>
The end of the actual octal escape sequence would be unrecognizable. So, GDB is doing you a service that it tells where the next character begins by escaping it.
If you put non-digits after the control characters, GDB does not need to escape them because they cannot be confused with the escape squence.