How Can I Declare an Array With a Variable Size in Standard C?

Dynamic Array Allocation in C with Variable Array Size

Variable-sized arrays, also known as dynamic arrays, pose a challenge in standard C. Consider the following program:

<br>int siz = 0;<br>int n = 0;<br>FILE* picture;</p>
<p>picture = fopen("test.jpg", "r");<br>fseek(picture, 0, SEEK_END);<br>siz = ftell(picture);</p>
<p>char Sbuf[siz];<br>fseek(picture, 0, SEEK_SET); //Going to the beginning of the file<br>while (!feof(picture)) {</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">n = fread(Sbuf, sizeof(char), siz, picture);
/* ... do stuff with the buffer ... */
/* memset(Sbuf, 0, sizeof(Sbuf)); */

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}

The code above attempts to allocate an array of characters with a size determined by a variable siz. However, in standard C, array sizes must be constants. This poses the question: how can we declare siz correctly to allow code compilation?

Unfortunately, there is no direct method to declare an array with a variable size in standard C. However, several alternatives exist:

• std::vector: In modern C , the std::vector container can be used as a flexible alternative to arrays. It can be easily extended to any desired size and its usage is relatively straightforward.
• New operator: The new operator can be employed to allocate memory dynamically on the heap. To create an array with a variable size, one can use char* Sbuf = new char[siz]; to allocate an array of siz characters on the heap. However, this approach introduces memory management concerns (e.g., potential memory leaks), making it less suitable than std::vector.

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