Export (0) Print
Expand All

String Literals Have Proper Type of const char[]

String literals now have the type const char [] and are now placed in a read-only section of memory. Changing that memory will now cause an access violation. Code compiled in previous versions using /GF will also cause the access violation.

The following sample compiles and runs in Visual Studio .NET but will fail at run time in Visual Studio .NET 2003:

// bc_string_literals_have_proper_type_of_const_char.cpp
// compile with: /c
void f(char *c) {
   c[0] = 'Q';   // Now gives run-time access violation
}

int main() {
   f("TEST");
}

In addition, the run-time behavior of code such as the following example has now changed:

// bc_string_literals_have_proper_type_of_const_char2.cpp
#include "stdio.h"
void f(const char *) {   // called in Visual Studio .NET 2003
   printf_s("in f(const char *)\n");
}

void f(char *) {   // called in Visual Studio .NET
   printf_s("in f(char *)\n");
}

int main() {
   f("TEST");
}

To resolve this error, do not pass string literals to functions where they will be modified.

For code that will be valid in the current and previous versions of Visual C++ in the case where functions are overloaded in this manner:

  • Explicitly cast string literals to const char*.

  • Define variables on the stack or the heap.

The following code will be valid in the Visual Studio .NET 2003 and Visual Studio .NET versions of Visual C++, causing an access violation in neither:

// bc_string_literals_have_proper_type_of_const_char3.cpp
#include <stdio.h>
void f(const char *psz) {
   printf_s("const version\n");
}

void f(char *psz) {
   printf_s("version where we modify it\n");
   psz[0] = 'x';
}

int main() {
   char myStr[] = "TEST";
   f((const char*)"TEST");
   f(myStr);
}

Community Additions

ADD
Show:
© 2014 Microsoft