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The behavior of this non-compliant example is undefined because the index i used to reference bs may be outside the range of bs, causing a write-out-of-bounds error.

string bs("01234567");
size_t i = f();

bs[i] = '\0';

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This compliant solution uses the {{basic_string at()}} method, which behaves in a similar fashion to the index {{operator\[\]}} but throws an {{out_of_range}} exception if {{pos >= size()}}.

string bs("01234567");
try {
  size_t i = f();
  bs.at(i) = '\0';
}
catch (...) {
  cerr << "Index out of range" << endl;
}

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The behavior of this non-compliant example is undefined because the size() of bs is 8 but the index used to reference bs ranges from 0 through 99.

string bs("01234567");
for (int i=0; i < 100; i++) {
  bs[i] = '\0';
}

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Use the fill algorithm to assign the value '\0' to evey element in the specified range:

size_t const max_fill = 100;
std::string bs("01234567");

fill(bs.begin(), bs.begin()+std::min(max_fill, bs.length()), '\0' );

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