C++ equivalent of Java >>>=? and problem with varint [duplicate]

Question

Here I have 2 functions one is in c++ and one is Java. Both have the same purpose: C++:

void VarIntToBufferArray(int* buffer, int in) { std::vector<int> buffVect; int value = in; do { int temp = (int)(value & 0b01111111); value >> 7; if (value != 0) { temp |= 0b10000000; } buffVect.push_back(temp); } while (value != 0); buffer = &buffVect[0]; }

Java:

public static void writeVarInt(int value) { do { byte temp = (byte)(value & 0b01111111); // Note: >>> means that the sign bit is shifted with the rest of the number rather than being left alone value >>>= 7; if (value != 0) { temp |= 0b10000000; } writeByte(temp); } while (value != 0); }

Something is wrong with C++ version of code because I get this output on C++: 0 0 99 -35 and on Java version: -35 -57 1 which should be. I think >> by itself can't replace >>>=. Any way of doing that?

value >> 7; is a no-op. Did you mean value >>= 7;? But for the equivalent of >>>, you probably need value = int(unsigned(value) >> 7); In Java, a separate operator for "unsigned shift" is needed because Java lacks unsigned integral types. — Igor Tandetnik
– Igor Tandetnik, Commented Nov 1, 2020 at 23:15
With value = int(unsigned(value) >> 7);, I get output: -858993460 -858993460 -858993460 -858993460 — INTmAker
– INTmAker, Commented Nov 1, 2020 at 23:23
What do you mean, you get output? The C++ code you've shown doesn't produce any output. In fact, the whole VarIntToBufferArray is an elaborate no-op, as it doesn't have any side effects. — Igor Tandetnik
– Igor Tandetnik, Commented Nov 1, 2020 at 23:26
int buffer[sizeof(int)]; VarIntToBufferArray(buffer, 25565); — INTmAker
– INTmAker, Commented Nov 1, 2020 at 23:27

INTmAker · Accepted Answer · 2020-11-01 23:37:48Z

Solved: (Now getting same output as in Java)

template<typename T> void convertUnderByteMax(T* temp) { if (*temp > 127) { *temp -= 256; } } void VarIntToBufferArray(std::vector<int>& buffer, int in) { int value = in; do { int temp = (int)(value & 0b01111111); value = ((unsigned int) value) >> 7; if (value != 0) { temp |= 0b10000000; } convertUnderByteMax(&temp); buffer.push_back(temp); } while (value != 0); }

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