warning: deprecated conversion from string constant to 'char*''

Question

I have declared the string array in my code as follows.

char *arr[] ={ 
"xyz",
"abc",
"pqr",
NULL
};

When compile then got following warning

warning: deprecated conversion from string constant to 'char*''

i know that "xyz" and other string literal are const char and my array is char* so have resolve it by declaring my array const char* arr but i loss the control to point this array in another pointer. So to resolve above issue have declared array as follows

 char *arr[] ={ 
    (char *)"xyz",
    (char *)"abc",
    (char *)"pqr",
    NULL
    };

But this type of declaration not fair when need large array (more then 100 string array). So any one have idea to resolve it by another way.

You have tagged this C++ (which is not the same language as C), so why not use a `std::vector` of `std::string`s? — JBentley, Jan 02 '14 at 12:59
The error message comes from a C++ compiler: this is valid in C but not in C++. — ouah, Jan 02 '14 at 13:08

score 4 · Accepted Answer · answered Jan 02 '14 at 12:58

You don't lose any re-pointing options by making the array a const char* arr[]. Note that there's a huge difference between const char * p (a mutable pointer to an immutable char) and a char * const p (an immutable pointer to a mutable char). This code is perfectly valid:

const char *arr[] = {
  "xyz",
  "abc",
  "pqr",
  NULL
};

arr[1] = "ghi";

Live example

Ivaylo Strandjev · Answer 2 · 2015-03-08T10:07:26.400

1

There is a difference between a const char* and char *const if your pointer is a const char* you can still point it to another location but you cannot modify the elements it contains. The correct solution in this case is to make the array const char*.

edited Mar 08 '15 at 10:07

answered Jan 02 '14 at 12:56

Ivaylo Strandjev

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4

I think you mean `char * const` for the second one. – Joseph Mansfield Jan 02 '14 at 12:58
no requirements for modifying it but require to traverse it by pointing it to another pointer. Have also tried it by declaring const char* but it cause the error at line where i assign address of above array to another pointer. – Jayesh Bhoi Jan 02 '14 at 13:01
@user3150853 is the pointer you assign to of another type? For instance if you try to point this array to an array of type `char * []` you will not succeed. – Ivaylo Strandjev Jan 02 '14 at 13:02
for example have assign above array to another char pointer like char *pp = arr. – Jayesh Bhoi Jan 02 '14 at 13:08
You can not assign a `char*` to a `const char*[]` these are two completely different types. It's like trying to assign an integer to an array of integers: `int a[2]; int b = a;` and of course this will never compile. – Ivaylo Strandjev Jan 02 '14 at 13:10
@jayeshbhoi You can type `const char* pp = arr;`. That should work. – rozina Jan 02 '14 at 13:34
@rozina You mean `const char* pp = arr[some_index];`, right? – Angew is no longer proud of SO Jan 02 '14 at 13:48
@Angew Yes I do :) Actually I didn't think it through. Thanks for correcting the mistake. – rozina Jan 02 '14 at 13:50

score 0 · Answer 3 · answered Jan 02 '14 at 13:01

0

String literals are constant, so you need const pointers to refer to them:

const char *arr[] = {
    // whatever
};

Historically, it used to be possible (but dangerous) to convert string literals to non-const char*, for compatibility with ancient code that didn't know about const. This conversion has been deprecated for many years, and finally removed from the language in 2011.

answered Jan 02 '14 at 13:01

Mike Seymour

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I don't think this post addresses the question OP apparently knows about `const char*` and literals but has problems using this type. – Ivaylo Strandjev Jan 02 '14 at 13:03
@IvayloStrandjev: If that is the case, the solution will depend very much on why there are "problems" with `const char*`; and should probably be solved by addressing those "problems", not by subverting the type system. – Mike Seymour Jan 02 '14 at 13:17
I agree. The question does not contain enough information to give a complete answer. – Ivaylo Strandjev Jan 02 '14 at 13:19

warning: deprecated conversion from string constant to 'char*''

3 Answers3