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POIssue with string to int conversion in C++
 

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  1. POIssue with string to int conversion in C++
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    <p>I have an application where I get a <code>vector&lt;string&gt;</code>. I need to iterate through each element in the vector and see if a value is an integer value.</p> <p>Although the vector represents strings, few of the elements can contain an integer. I need to figure out which of those elements are integers, and if an element is an integer, I need its value. If an element in the vector is a string, then I just ignore it.</p> <p>I tried to use <code>atoi(vector[index].c_str())</code>, but I have an issue with it. <code>atoi</code> returns an integer value if the value contained in the string is an integer. If not, it returns 0</p> <p>So, consider the following:</p> <pre><code>atoi("Shankar") = 0 atoi("0") = 0 </code></pre> <p>and</p> <pre><code>atoi("123") = 123 atoi("123Shankar") = 123 </code></pre> <p>So, how do I distinguish between the above shown cases? If this cannot be achieved using atoi, then what is the alternate solution to this problem?</p> <p>Please assist.</p> <p><strong>EDIT</strong>:</p> <p>I can loop through the string and see if every character is an integer, but that reduces performance, since for m strings with an average of n characters, I need to check m X n times which makes it O(n^2).</p> <p>is there a better way to solve this problem?</p> <p><strong>EDIT2</strong>:</p> <p>Unfortunately, I cannot use any 3rd party library for this and just use STL</p> <p><strong>EDIT3</strong>:</p> <p>In my application, the vector does not contain any negative integers so I am considering Xeo's solution since sstream does not distinguish between "123" and "123Shankar"</p> <p>Thanks everyone for your assistance.</p>
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    1. USShankar Raju
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    1. COremoved C tag as this has nothing to do with C
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      1. USjk.
    2. COMy bad! I thought if there is some solution for this in C, then it also exists in C++ and hence put it there. Anyways, thanks for the edit
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      1. USShankar Raju
    3. CO_I can loop through the string and see if every character is an integer, but that reduces performance, since for m strings with an average of n characters, I need to check m X n times which makes it O(n^2)._ I don't believe that's a fair characterization of the performance of looping over the _m_ strings of your vector, or of the performance of scanning the _m * n_ characters of your collection of strings. In each case, it's still a linear scan of your input, and I don't think you can claim it's O(n^2)
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      1. USJerry Asher
 

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