通过unique_ptr访问结构成员会产生分段错误 [英] Accessing struct member through unique_ptr gives segmentation fault

问题描述

这就是我将指针设置为struct的方式.在运行时，分段错误在第二行引发.LoadedPDFInfo是Canvas命名空间中的结构

This is how I set pointer to struct. At runtime segmentation fault is thrown at second line. LoadedPDFInfo is struct in Canvas namespace

struct std::unique_ptr<Canvas::LoadedPDFInfo> pdfInfo;
pdfInfo->handle = ++currentPDFHandle;
pdfInfo->totalPageNum = FPDF_GetPageCount(doc);

推荐答案

首先， std :: unique_ptr 是 class 而不是 struct ，因此请删除 pdfInfo 变量声明上的 struct 前缀.您可能正想着这个:

First, std::unique_ptr is a class not a struct, so get rid of the struct prefix on the pdfInfo variable declaration. You were probably thinking of this instead:

std::unique_ptr<struct Canvas::LoadedPDFInfo> pdfInfo;

但是，即使使用实际的 struct 类型声明变量(或类型转换)，您仍然不需要 struct 前缀.C需要，而C ++不需要.

But even when declaring variables (or type-casting) using actual struct types, you still do not need the struct prefix. C needs that, C++ does not.

第二，发生段错误是因为您仅声明了 pdfInfo 变量，但实际上并未指向有效的 LoadedPDFInfo 对象，因此请使用-> 运算符无效.就像常规指针一样， std :: unique_ptr (以及 std :: auto_ptr 和 std :: shared_ptr )必须指向进入某事，以便访问该某事的成员.例如:

Second, your segfault is happening because you have merely declared the pdfInfo variable, but it is not actually pointing at a valid LoadedPDFInfo object, so using the -> operator is not a valid operation. Just like a regular pointer, std::unique_ptr (and std::auto_ptr, and std::shared_ptr) have to point at something in order to access that something's members. For example:

std::unique_ptr<Canvas::LoadedPDFInfo> pdfInfo(new Canvas::LoadedPDFInfo);

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