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    <p>When you write a "string" in your source code, it gets written directly into the executable because that value needs to be known at compile time (there are tools available to pull software apart and find all the plain text strings in them). When you write <code>char *a = "This is a string"</code>, the location of "This is a string" is in the executable, and the location a points to, is in the executable. The data in the executable image is read-only.</p> <p>What you need to do (as the other answers have pointed out) is create that memory in a location that is not read only--on the heap, or in the stack frame. If you declare a local array, then space is made on the stack for each element of that array, and the string literal (which is stored in the executable) is copied to that space in the stack.</p> <pre><code>char a[] = "This is a string"; </code></pre> <p>you can also copy that data manually by allocating some memory on the heap, and then using <code>strcpy()</code> to copy a string literal into that space.</p> <pre><code>char *a = malloc(256); strcpy(a, "This is a string"); </code></pre> <p>Whenever you allocate space using <code>malloc()</code> remember to call <code>free()</code> when you are finished with it (read: memory leak).</p> <p>Basically, you have to keep track of where your data is. Whenever you write a string in your source, that string is read only (otherwise you would be potentially changing the behavior of the executable--imagine if you wrote <code>char *a = "hello";</code> and then changed <code>a[0]</code> to <code>'c'</code>. Then somewhere else wrote <code>printf("hello");</code>. If you were allowed to change the first character of <code>"hello"</code>, and your compiler only stored it once (it should), then <code>printf("hello");</code> would output <code>cello</code>!)</p>
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    1. POIs it possible to modify a string of char in C?
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    1. USCarson Myers
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    1. POIs it possible to modify a string of char in C?
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    1. COThe last section explained me a lot on why that needs to be readonly. Thank you.
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    2. CO-1: doesn't tell to use const char*, and nothing guarantees that literal strings are stored in executable memory.
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      1. USBastien Léonard
    3. COI don't you don't need const for the two solutions I've given--also, if the string is known at compile time, and compiled into the executable--where else would it get stored? In gcc, if I write either char *a = "hallo."; or char b[] = "hello.";, then the assembly outputs "LC0: .ascii "Hallo.\0" LC1: .ascii "Hello.\0"" both are in executable memory... When is it not?
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