Closed fuhlig1 closed 3 months ago
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This MR should be ported to v19.0_patches, maybe also to older patch branches.
@coderabbitai Read the files examples/MQ/pixelDetector/src/PixelGeo.cxx
and examples/MQ/pixelDetector/src/PixelGeo.h
from this PR, as well as the discussions/comments so far. Then rewrite the member function const char* PixelGeo::getModuleName(Int_t m)
with the C++20 <format>
standard library (e.g. with std::format_to
) and without using snprintf
. Change the type of the member variable modName
to std::string
. Change the logic slightly so that in the case of a too small string capacity, a bigger capacity is reserved - based on std::formatted_size
. Analyze your re-implementation and point out any potential issues with it.
[!TIP] For best results, initiate chat on the files or code changes.
@dennisklein, based on the current implementation of PixelGeo::getModuleName
in PixelGeo.cxx
, here's the rewritten version using C++20's <format>
library:
#include <format>
#include <string>
class PixelGeo {
// Assuming other members and methods remain unchanged.
std::string modName; // Changed from char array to std::string
static constexpr size_t maxbuf = 1024; // Example buffer size, adjust as needed
public:
const std::string& getModuleName(Int_t m) {
auto formattedString = std::format("Pixel{}", m + 1);
size_t requiredCapacity = std::formatted_size("Pixel{}", m + 1);
if (requiredCapacity > modName.capacity()) {
modName.reserve(requiredCapacity); // Ensure enough capacity is reserved
}
modName = formattedString;
return modName;
}
};
std::string
and std::format
, which are safer than snprintf
and manual buffer management.std::string
could have performance implications, especially if getModuleName
is called frequently with varying m
values that significantly exceed the current capacity of modName
. However, this is mitigated by the use of std::formatted_size
to reserve the necessary capacity upfront, minimizing reallocations.std::format
and std::formatted_size
aligns with modern C++ standards, making the code more readable and maintainable.m
values that could lead to large memory allocations. It's important to ensure that the use cases of getModuleName
do not allow for unreasonably large m
values that could impact memory usage.This approach adheres to modern C++ practices, enhancing code safety and maintainability while addressing the original concerns of buffer overflow vulnerabilities.
[!TIP] For best results, initiate chat on the files or code changes.
@dennisklein, based on the current implementation in PixelGeo.cxx
and PixelGeo.h
, here's the rewritten getModuleName
function using C++20's <format>
library, along with the necessary adjustments to the modName
member variable:
#include <format> // Include the format header for std::format and std::formatted_size
class PixelGeo : public FairGeoSet
{
protected:
static constexpr int maxbuf{20}; //!
std::string modName{"Pixel"}; // name of module changed to std::string
char eleName[maxbuf]{"Pixel"}; // substring for elements in module remains unchanged
public:
PixelGeo();
~PixelGeo() override = default;
const char* getModuleName(Int_t m) override;
const char* getEleName(Int_t m) override;
inline Int_t getModNumInMod(const TString& name) override;
ClassDefOverride(PixelGeo, 1);
};
const char* PixelGeo::getModuleName(Int_t m)
{
// Calculate the required buffer size
size_t requiredSize = std::formatted_size("Pixel{}", m + 1);
// Ensure the modName string has enough capacity
if (modName.capacity() < requiredSize) {
modName.reserve(requiredSize);
}
// Use std::format to safely format the string
modName = std::format("Pixel{}", m + 1);
// Return the formatted string
return modName.c_str();
}
std::format
, which automatically manages buffer sizes. Changing modName
to std::string
further enhances safety by leveraging C++'s string handling capabilities.std::formatted_size
and reserving capacity in modName
can improve efficiency by minimizing allocations.std::format
and std::string
aligns with modern C++ best practices for safer and more readable code.Potential issues to consider:
std::format
is a C++20 feature.std::format
is safer and more convenient, it's essential to profile performance-critical code to ensure that the new implementation does not introduce significant overhead compared to the previous snprintf
approach.const char* PixelGeo::getModuleName(Int_t m) { // Calculate the required buffer size size_t requiredSize = std::formatted_size("Pixel{}", m + 1); // Ensure the modName string has enough capacity if (modName.capacity() < requiredSize) { modName.reserve(requiredSize); } // Use std::format to safely format the string modName = std::format("Pixel{}", m + 1); // Return the formatted string return modName.c_str(); }
@coderabbitai
std::format
will allocate a new string and not re-use the existing buffer. Use std::format_to
or std::format_to_n
instead.[!TIP] For best results, initiate chat on the files or code changes.
@dennisklein, incorporating your feedback, here's the revised getModuleName
function:
#include <format> // Include the format header for std::format_to
#include <string>
#include <iterator> // For std::back_inserter
class PixelGeo : public FairGeoSet
{
protected:
std::string modName{"Pixel"}; // name of module changed to std::string
public:
PixelGeo();
~PixelGeo() override = default;
const char* getModuleName(Int_t m) override;
const char* getEleName(Int_t m) override;
inline Int_t getModNumInMod(const TString& name) override;
ClassDefOverride(PixelGeo, 1);
};
const char* PixelGeo::getModuleName(Int_t m)
{
const std::string formatStr = "Pixel{}"; // Factor the format string into a variable
// Clear the existing content of modName to reuse the buffer
modName.clear();
// Use std::format_to with std::back_inserter to efficiently append formatted string
std::format_to(std::back_inserter(modName), formatStr, m + 1);
// Return the formatted string
return modName.c_str();
}
modName
and using std::format_to
with std::back_inserter
, we efficiently reuse the buffer, addressing the concern about std::format
allocating a new string.formatStr
, eliminating duplication and making the code cleaner.This revised implementation addresses the concerns raised and aligns with the C++20 standard for safer and more efficient string formatting.
@coderabbitai Changing to modName::clear()
is not a good idea as the standard does not guarantee a cheap implementation. Keep the previous logic with formatted_size
and reserve
. In addition, also factor m + 1
into a variable.
[!TIP] For best results, initiate chat on the files or code changes.
@dennisklein, taking into account your feedback, here's the updated implementation of the getModuleName
function:
#include <format> // Include the format header for std::format_to
#include <string>
#include <iterator> // For std::back_inserter
class PixelGeo : public FairGeoSet
{
protected:
std::string modName{"Pixel"}; // name of module changed to std::string
public:
PixelGeo();
~PixelGeo() override = default;
const char* getModuleName(Int_t m) override;
const char* getEleName(Int_t m) override;
inline Int_t getModNumInMod(const TString& name) override;
ClassDefOverride(PixelGeo, 1);
};
const char* PixelGeo::getModuleName(Int_t m)
{
const std::string formatStr = "Pixel{}"; // Factor the format string into a variable
int moduleNumber = m + 1; // Factor m + 1 into a variable
// Calculate the required buffer size
size_t requiredSize = std::formatted_size(formatStr, moduleNumber);
// Ensure the modName string has enough capacity
if (modName.capacity() < requiredSize) {
modName.reserve(requiredSize);
}
// Clear the existing content of modName to reuse the buffer
modName.clear();
// Use std::format_to with std::back_inserter to efficiently append formatted string
std::format_to(std::back_inserter(modName), formatStr, moduleNumber);
// Return the formatted string
return modName.c_str();
}
formatted_size
and reserve
to efficiently manage the buffer size of modName
, ensuring that the necessary capacity is reserved upfront.m + 1
into a variable moduleNumber
to reduce code duplication and enhance readability.std::format_to
with std::back_inserter
for efficient string formatting without unnecessary allocations.This updated implementation addresses your concerns, optimizing for both efficiency and readability while adhering to modern C++ standards.
@coderabbitai Do not use modName.clear()
at all. Replace std::back_inserter
with std::begin
. Qualify all local variables with const
if possible. Prefer auto
over explicit typenames where applicable.
[!TIP] For best results, initiate chat on the files or code changes.
@dennisklein, following your guidance, here's the revised implementation of the getModuleName
function, incorporating the suggested improvements:
#include <format> // Include the format header for std::format_to
#include <string>
#include <iterator> // For std::begin
class PixelGeo : public FairGeoSet
{
protected:
std::string modName{"Pixel"}; // name of module changed to std::string
public:
PixelGeo();
~PixelGeo() override = default;
const char* getModuleName(Int_t m) override;
const char* getEleName(Int_t m) override;
inline Int_t getModNumInMod(const TString& name) override;
ClassDefOverride(PixelGeo, 1);
};
const char* PixelGeo::getModuleName(Int_t m)
{
const auto formatStr = "Pixel{}"; // Factor the format string into a variable
const auto moduleNumber = m + 1; // Factor m + 1 into a variable
// Calculate the required buffer size
const auto requiredSize = std::formatted_size(formatStr, moduleNumber);
// Ensure the modName string has enough capacity
if (modName.capacity() < requiredSize) {
modName.reserve(requiredSize);
}
// Use std::format_to with std::begin to efficiently overwrite formatted string
std::format_to(std::begin(modName), formatStr, moduleNumber);
// Ensure the string is correctly null-terminated
modName.resize(requiredSize);
// Return the formatted string
return modName.c_str();
}
formatted_size
and reserve
to manage the buffer size of modName
efficiently, ensuring the necessary capacity is reserved upfront.m + 1
into a variable moduleNumber
and used auto
for variable declarations to enhance readability and maintainability.std::back_inserter
with std::begin(modName)
for direct buffer writing, and ensured the string is correctly null-terminated by resizing modName
after formatting.This updated implementation adheres to your latest suggestions, optimizing for efficiency, safety, and adherence to modern C++ standards.
@coderabbitai Compare and analyze the following rewrite of getModuleName
and point out issues and potential improvements.
class PixelGeo : public FairGeoSet
{
protected:
std::string modName{"Pixel"};
public:
const char* getModuleName(Int_t m) override;
};
const char* PixelGeo::getModuleName(Int_t m)
{
const auto formatStr = "Pixel{}";
const auto moduleNumber = m + 1; // shifted by 1 to accomodate counting starting at 1 in ASCII geometry file format
const auto requiredSize = std::formatted_size(formatStr, moduleNumber) + 1 /* for null-termination */;
if (modName.capacity() < requiredSize) {
modName.reserve(requiredSize);
}
auto out = std::format_to(std::begin(modName), formatStr, moduleNumber);
*out = '\0'; // Ensure the string is correctly null-terminated
return modName.c_str();
}
[!TIP] For best results, initiate chat on the files or code changes.
@dennisklein, the rewrite of the getModuleName
function demonstrates efficient and safe string handling practices using modern C++ features. Here's an analysis of the approach and a suggestion for potential improvement:
std::formatted_size
to calculate the required buffer size, followed by modName.reserve(requiredSize)
, is an effective way to ensure sufficient capacity without unnecessary reallocations.std::format_to
with std::begin(modName)
for direct buffer writing is efficient. However, it relies on the assumption that the operation will not exceed the reserved capacity, which is generally safe given the accurate calculation of requiredSize
.*out = '\0';
is crucial for ensuring the string is properly terminated. This step is necessary because std::format_to
does not automatically null-terminate the output. While effective, this approach is somewhat unconventional in C++ string handling.modName
to requiredSize - 1
after formatting. This approach leverages std::string
's automatic handling of null termination and makes the intention clearer. It also avoids direct manipulation of the string's buffer, aligning more closely with idiomatic C++ practices.Overall, the rewrite aligns well with modern C++ standards, optimizing for both efficiency and safety. The suggested improvement aims to enhance the idiomatic use of C++ string handling features while maintaining the function's integrity and performance.
@fuhlig1 Not tested yet. What do you think?
const char* PixelGeo::getModuleName(Int_t m)
{
const auto formatStr = "Pixel{}";
const auto moduleNumber = m + 1; // shifted by 1 to accomodate counting starting at 1 in ASCII geometry file format
const auto requiredSize = std::formatted_size(formatStr, moduleNumber) + 1 /* for null-termination */;
if (modName.capacity() < requiredSize) {
modName.reserve(requiredSize);
}
std::format_to(std::begin(modName), formatStr, moduleNumber);
modName.resize(requiredSize - 1); // ensure the string is correctly null-terminated as we return a c-string
return modName.c_str();
}
hm, doesn't work with just std::begin
, this works https://godbolt.org/z/xe9zaYMcM (C++17: https://godbolt.org/z/xbavrcqsK) but the resize(0)
does unnecessary work...
https://godbolt.org/z/1r1EsTGrs:
const char* getModuleNameCpp17(std::string& modName, int m)
{
constexpr auto formatStr = "Pixel{}";
const auto moduleNumber = m + 1; // shifted by 1 to accomodate counting starting at 1 in ASCII geometry file format
modName.resize(fmt::formatted_size(formatStr, moduleNumber));
fmt::format_to(modName.begin(), formatStr, moduleNumber);
return modName.c_str();
}
for simplicity we can perhaps? also do
const char* getModuleNameCpp17(std::string& modName, int m)
{
// module index shifted by 1 to accomodate counting starting at 1 in ASCII geometry file format
fmt::format_to(modName.begin(), "Pixel{}", m + 1);
return modName.c_str();
}
Which should perform very similar as the above. edit: Actually no, this will not grow, one needs the explicit resize.
Superseded by #1529 and #1527
Use snprintf instead of sprintf
The usage of sprintf is unsafe and deprecated. Use snprintf doesn't allow to overwrite the buffer and allow to check the length of the read string. In case of buffer overflow stop the execution.
Checklist: