If I want to construct a std::string with a line like:
std::string my_string("a\0b");
Where i want to have three characters in the resulting string (a, null, b), I only get one. What is the proper syntax?
Yes you can have embedded nulls in your std::string .
c_str() method, you get an array of characters with the '\0' character at the end. @alegen none of that changes anything. Usually \0 indicates the end of a string. So if you pass c_str() with nulls in the middle to a function expecting a null terminated string it won't use the full string, just up to the first null.
'\0' is defined to be a null character. It is a character with all bits set to zero.
A string can be made up of only a null character.
we have been able to create literal std::string
#include <iostream> #include <string> int main() { using namespace std::string_literals; std::string s = "pl-\0-op"s; // <- Notice the "s" at the end // This is a std::string literal not // a C-String literal. std::cout << s << "\n"; }
The problem is the std::string
constructor that takes a const char*
assumes the input is a C-string. C-strings are \0
terminated and thus parsing stops when it reaches the \0
character.
To compensate for this, you need to use the constructor that builds the string from a char array (not a C-String). This takes two parameters - a pointer to the array and a length:
std::string x("pq\0rs"); // Two characters because input assumed to be C-String std::string x("pq\0rs",5); // 5 Characters as the input is now a char array with 5 characters.
Note: C++ std::string
is NOT \0
-terminated (as suggested in other posts). However, you can extract a pointer to an internal buffer that contains a C-String with the method c_str()
.
Also check out Doug T's answer below about using a vector<char>
.
Also check out RiaD for a C++14 solution.
If you are doing manipulation like you would with a c-style string (array of chars) consider using
std::vector<char>
You have more freedom to treat it like an array in the same manner you would treat a c-string. You can use copy() to copy into a string:
std::vector<char> vec(100) strncpy(&vec[0], "blah blah blah", 100); std::string vecAsStr( vec.begin(), vec.end());
and you can use it in many of the same places you can use c-strings
printf("%s" &vec[0]) vec[10] = '\0'; vec[11] = 'b';
Naturally, however, you suffer from the same problems as c-strings. You may forget your null terminal or write past the allocated space.
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