"Strange" access violation writing error c++
Author
Hi,
it seems that I have a problem with a c++ rtrim (removes spaces from a string on the right side) function I borrowed from dosbox source code. The function implementation is the following:
char *rtrim(char *str)
{
char *p;
p = strchr(str, '\0');
while(--p>=str && isspace(*reinterpret_cast<unsigned char *>(p)));
p[1] = '\0';
return str;
}
Compiling is fine, when debugging I get :
Unhandled exception at 0x0041756c in test.exe: 0xC0000005: Access violation writing location 0x0041d803
on the p[1]='\0' assignment, even if the assignment in the immediate window works just fine. I use visual studio 2008. Any ideas would be appreciated, thanks in advance.
char *rtrim(char *str){ for (char *p = strchr(str, '\0') - 1 ; p >= str && isspace(*p) ; --p) *p = '\0'; return str;}(untested)
Anyway, I think p[1] is the problem.
Also, what do you pass to rtrim? You can't do something like:
char* trimmed = rtrim("test string ");
Author
Quote:Original post by janta
Anyway, I think p[1] is the problem.
Thanks for the quick answer, indeed p[1]='\0' is the problem.
Quote:
Also, what do you pass to rtrim? You can't do something like:char* trimmed = rtrim("test string ");
That's exactly what I pass, why would it be a problem? Just a reminder, everything works fine in immediate window, p[1] assignment is ok and str pointer indeed holds the trimmed string after the assignment, that's why I am confused with this.
Modifying a character literal is undefined/implementation defined behavior.
In fact it should't compile because
is const.
However doing
is ok.
In fact it should't compile because
"test string "is const.
However doing
char str[] = "test string ";rtrim(str);is ok.
Did you mean C? Because in C++ we prefer to avoid playing with raw character arrays.
std::string rtrim(const std::string &str){ std::string::size_type index = str.find_last_not_of(' '); return str.substr(0,index == std::string::npos ? index : index + 1);}
However, a space is not the only type of white space the OP might want to avoid. ('\r', '\n', '\t'...)
And the op's function modifies the string in-place even when not assigning the result back to the original value.
I'm not implying that an idiomatic C++ equivalent version can't be written.
And the op's function modifies the string in-place even when not assigning the result back to the original value.
I'm not implying that an idiomatic C++ equivalent version can't be written.
It is a fairly easy thing to add to that code, what with std::string::find_last_not_of having an overload that accepts a string of characters to match. Doing that is left as an exercise to the OP [smile]
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