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Can anyone tell me why setprecision is causing this error at runtime:

terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc
Aborted

The program ran fine; after I added << setprecision(2) << to a series of output, I received the error when trying to run the program. I have included iomanip and the program will run fine if I remove the setprecision manipulator. Thanks for any help.

Here is the snippet of code where I'm trying to use setprecision, avgWait is a float variable:

//Calculate average waiting time,
  //.005 added to round to nearest hundreth of a time unit
  avgWait = ((float)totalWait/totCust) + .005;
  
  cout<< endl << "The simulation ran for " << sTime << " time units" << endl
      << "Number of servers: " << numServers << endl
      << "Average transaction time: " << tTime << endl
      << "Average time between customer arrivals: " << tbArrival << endl
      << "Total waiting time: " << totalWait << endl
      << "Number of customers that completed a transaction: " << servedCust
      << endl
      << "Number of customers left at servers: "
      << servers.getNumberOfBusyServers() << endl
      << "Number of customers left in the queue: " << customers.size() << endl
      << "Average waiting time: " << fixed << setprecision(2) << avgWait << endl
      << "***************END SIMULATION***************" << endl;
Edited by bgx90 because: n/a
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Dani AI

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Given 's follow-up that the exception went away after fixing other bugs, the most likely explanation is not a bug in the manipulator itself but latent undefined behaviour (heap corruption, out‑of‑bounds access, use-after-free, etc.) being exposed by a change in program execution. The setprecision manipulator and the iostream formatting path can touch locale/formatting code and trigger allocations that previously never occurred; if allocator metadata is already corrupt, the first allocation can throw std::bad_alloc. See and the setprecision reference for background.

Practical steps to find the real fault:

  • Run with AddressSanitizer or Valgrind to catch heap corruption, buffer overruns, and use-after-free. Example tools: AddressSanitizer and Valgrind.
  • Build libstdc++ in debug mode to detect invalid container usage: compile with -D_GLIBCXX_DEBUG.
  • Turn on iostream exceptions and catch them to see where stream code fails.

Example commands and small patterns to try:

g++ -g -O1 -fsanitize=address,undefined -fno-omit-frame-pointer main.cpp -o main
valgrind --leak-check=full --track-origins=yes ./main
g++ -g -O0 -D_GLIBCXX_DEBUG main.cpp -o main
cout.exceptions(std::ios::badbit | std::ios::failbit);
try {
    // your output statements here
} catch (const std::exception& e) {
    cerr << "i/o exception: " << e.what() << '\n';
}

Quick checklist before deep debugging: ensure denominators are nonzero, validate indices and iterators, check lifetime of objects used in output, and look for mismatched new/delete. Because fixing other bugs removed the failure, the root cause was almost certainly elsewhere; use sanitizers and a minimal reproducer to find it so setprecision can stay in place safely.

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Edited by Schrödinger because: n/a
Member Avatar for bgx90

After fixing other seemingly unrelated problems with the program, the error stopped occurring. Still, it would be nice to know how just adding the setprecision manipulator caused this error.

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