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I was recently trying to track down some bugs in a program I am working on using valgrind, and one of the errors I got was:
==6866== Invalid write of size 4
==6866== at 0x40C9E2: superneuron::read(_IO_FILE*) (superneuron.cc:414)
the offending line # 414 reads
amplitudes__[points_read] = 0x0;
and amplitudes__ is defined earlier as
uint32_t * amplitudes__ = (uint32_t* ) amplitudes;
Now obviously a uint32_t is 4 bytes long, so this is the write size, but could someone tell me why it's invalid ?
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An Invalid read means that the memory location that the process was trying to read is outside of the memory addresses that are available to the process. size 8 means that the process was trying to read 8 bytes. On 64-bit platforms this could be a pointer, but also for example a long int.
“Invalid write” means that our program tries to write data in a memory zone where it shouldn't. But Valgrind tells you way more than that. It first tells you the size of the written data, which is 1 bytes, and corresponds to the size of a character.
Look for function names and line numbersIf you compile your program with the -g flag, Valgrind will show you the function names and line numbers where errors occur.
Valgrind (/ˈvælɡrɪnd/) is a programming tool for memory debugging, memory leak detection, and profiling. Valgrind. Original author(s)
points_read is most likely out of bounds, you're writing past (or before) the memory you allocated for amplitudes.
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