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How Do C++ Compilers Merge Identical String Literals

Asked 2011-06-08T16:06:09.503
17

How does compiler (MS Visual C++ 2010) combine identical string literals in different cpp source files? For example, if I have the string literal "hello world\n" in src1.cpp and src2.cpp respectively. The compiled exe file will have only 1 "hello world" string literal probably in the constant/readonly section. Is this task done by the linker?

What I hope to achieve is that I got some modules written in assembly to be used by C++ modules. And these assembly modules contain many long string literal definitions. I know the string literals are identical to some other string literals in the C++ source. If I link my assembly generated obj code with the compiler generated obj code, would these string literals be merged by the linker to remove redundant strings as is the case when all modules are in C++?

c++ visual-c++ compiler-construction linker
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Assembly language doesn't provide any way to work directly with an anonymous string literal like C or C++ does.

As such, what you almost certainly want to do is define the strings in your assembly code with names. To use those from C or C++, you want to put an extern declaration of the array into a header that you can #include in whatever files need access to them (and in your C++ code, you'll use the names, not the literals themselves):

foo.asm

.model flat, c

.data
    string1 db "This is the first string", 10, 0
    string2 db "This is the second string\n", 10, 0

foo.h:

extern char string1[];
extern char string2[];

bar.cpp

#include "foo.h"

void baz() { std:::cout << string1; }
answered 2011-06-08T18:31:31.237

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