Thread: where the "String literals" store in ?

EX:
char string[50] = "liyanhong";

I konw 'string' will store in where called the Stack, but the String literals "liyanhong" where does it store ?

My English is bad, please don't mind

Data segment - Wikipedia, the free encyclopedia

Thanks

String literals could be stored in the data segment or code segment. It's up to the compiler. As code-segment is at least read-access, I don't see a problem if during execution data is copied from there.

Originally Posted by liyanhong

EX:
char string[50] = "liyanhong";

I konw 'string' will store in where called the Stack, but the String literals "liyanhong" where does it store ?

The answer depends on where the array string[] is defined.
If it's defined inside a function, then "liyanhong" will be stored in the stack segment.
If it's defined outside of any function, then "liyanhong" will be stored in the data segment.
However, a string literal defined as

Code:

char *s = "liyanhong";

will be stored in the text segment, tho' some compilers have switches to modify that behavior.
That's also the reason why a string literal can't be altered since the text segment is readonly.

Thank you, I will always come to study here later.

In GCC:

Code:

char writablestring[]="string"; /* This goes in the data seg and is writable */
char *nonwritablestring="string"; /* This goes before the function in the code seg and is not writable, writing to it will cause a seg fault*/

GCC used to accept the -fwritable-strings option to specify that all strings should be writable, as of 4.0, this is no longer maintained.

quzah: In any cases you, I, or OP are likely to encounter, without directly searching for exceptions, what I said will hold true. Of coarse there are going to be exceptions, for example, one could mark the segment as writable and executable(I don't know how to specify to the linker that this is desired, but it is possible. Fasm has a directive to make your '.text' or any other segment executable.)

nonoob: No compiler I've ever heard of, including GCC, supports far pointers(pointers that use segments). All pointers used by GCC use the DS register(the one used when none is specified). The term seg fault is an outdated term from the stone age when segmentation was used(Windows and Linux use a flat memory model, with no segmentation, just one big segment). A seg fault is actually when a process accesses a page incorrectly. Pages can be marked writable, readable, and/or executable. Paging is the main form of memory protection in ALL modern operating systems. You can allocate a page in Windows with VirtualAlloc. Pages allocated can be even be marked in a way that would allow you to write to all strings and code! SMC is still possible.

Originally Posted by quzah

My point is, the standard doesn't say that string literals cannot be writable.

Touche. Good point, I didn't think to consult the standards.