How can I check for string prefixes and convert substrings to integers in C ?

Exact String Matching and Substring Conversion in C

To determine if a C std::string begins with a given string, as in the Python example provided, use the rfind overload that accepts a search position parameter. Here's how:

<code class="cpp">std::string s = "tititoto";
if (s.rfind("titi", 0) == 0) { // pos=0 limits search to the prefix
    // s starts with the prefix
}</code>

C 20 and later introduced the starts_with method, simplifying the process:

<code class="cpp">std::string s = "tititoto";
if (s.starts_with("titi"s)) { // "s" suffix creates a std::string_view
    // s starts with the prefix
}</code>

Now, let's consider the int conversion. In the original Python code, a substring is extracted using the slice notation [len('--foo='):]. To achieve the same in C , use the substr method:

<code class="cpp">std::string argv1 = "--foo=98";
std::string foo_value_str = argv1.substr(argv1.find("=") + 1);
int foo_value = std::stoi(foo_value_str);</code>

By using these techniques, you can check for string prefixes and convert substrings to integers efficiently in C .

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