On 4/8/06, Lynn Allan wrote:

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Sorry if this is off-topic.

Just wanted to check .... are std::string's defined to be null terminated?

I came across a web page that indicated they are, but you can find lots of misinformation on the web. http://www.codeproject.com/string/cppstringguide2.asp

std::string's seem to be null terminated with the Microsoft vc7.1 and vc8 compiler, but I wanted to check if this is generally true according to the C++ standard.

I'm relatively new to stl and using std::string .... mostly have used C strings and MFC CStrings (which changed from vc6 to vc7.1?)

From: "Olaf van der Spek"

std::string::c_str() returns a pointer to a null-terminated string, yes.

Thanks, but that isn't quite my question. I'm interested in the actual internal layout of the data in the actual std::string. I realize that myString.c_str() returns a null terminated string, but my understanding is that the result of c_str() can be a separate buffer, not necessarily a pointer to the buffer used by the std::string. Does the internal data structure of the std::string itself have null termination, by definition of the C++ standard? I looked a little harder, and the vc7.1 and vc8 documentation for std::string.c_str() states: Objects of type string belonging to the C++ template class basic_string<char> are not necessarily null terminated. The null character ' \0 ' is used as a special character in a C-string to mark the end of the string but has not special meaning in an object of type string and may be a part of the string just like any other character. There is an automatic conversion from const char* into strings, but the string class does not provide for automatic conversions from C-style strings to objects of type basic_string<char>. But it seems like the vc7.1 implementation of c_str provides the actual address of the internal buffer: std::string strC("HIJKL"); pTest = strC.c_str(); for (int i = 0; i < 80; ++i) { printf("I: %2d Address: %d ch:%3d %c\n", i, &pTest[i], pTest[i], pTest[i]); } printf("\n********************\n"); printf("Sizeof std::stringC: %d\n", sizeof(strC)); printf("&strC: %d\n", &strC); printf("strC.c_str(): %d\n", strC.c_str()); printf("(const char*)strC.c_str(): %d\n", (const char*)strC.c_str()); char* pNonConst = (char*)pTest; pNonConst[3] = 'X'; printf("%s %s %s\n", strC.c_str(), pTest, pNonConst); results in: HIJXL HIJXL HIJXL

On 4/8/06, Lynn Allan wrote: Thanks, but that isn't quite my question. I'm interested in the actual internal layout of the data in the actual std::string.

The standard doesn't force any internal representation for std::string. It could be a linked list of characters, if the implementation felt like being evil. ( More likely would be a rope of some kind. ) I would expect, however, that most implementations wil basically keep it as a null-terminated std::vector<char>-like internal representation for simplicity since c_str() is unfortunatly still rampant. ~ Scott

At 10:42 2006-04-08, Lynn Allan wrote:

...

On 4/8/06, Lynn Allan wrote:

...

Sorry if this is off-topic.

Just wanted to check .... are std::string's defined to be null terminated?

I came across a web page that indicated they are, but you can find lots of misinformation on the web. http://www.codeproject.com/string/cppstringguide2.asp

std::string's seem to be null terminated with the Microsoft vc7.1 and vc8 compiler, but I wanted to check if this is generally true according to the C++ standard.

I'm relatively new to stl and using std::string .... mostly have used C strings and MFC CStrings (which changed from vc6 to vc7.1?)

From: "Olaf van der Spek"

...

std::string::c_str() returns a pointer to a null-terminated string, yes.

Thanks, but that isn't quite my question. I'm interested in the actual internal layout of the data in the actual std::string.

bad idea all around. there are no guarantees of an internal layout for std::string. I'm curious, though, _why_ are you interested?

[bunch of irrelevant stuff deleted]

Victor A. Wagner Jr. http://rudbek.com The five most dangerous words in the English language: "There oughta be a law"

Thanks, but that isn't quite my question. I'm interested in the actual internal layout of the data in the actual std::string.

I realize that myString.c_str() returns a null terminated string, but my understanding is that the result of c_str() can be a separate buffer, not necessarily a pointer to the buffer used by the std::string. Does the internal data structure of the std::string itself have null termination, by definition of the C++ standard?

No it doesn't have to have the NULL character at the end, and I believe at least some versions of libstdc++ don't put the NULL on the end unless you call c_str(). John.