如何安全地从int转换为size_t? [英] How can I convert to size_t from int safely?

问题描述

在GCC中将int分配给size_t(或在malloc中使用它)会产生以下警告:

Assigning an int to a size_t (or using it in malloc) in GCC produces the following warning:

警告:从"int"转换为"size_t"可能会更改结果的符号[-Wsign-conversion]

warning: conversion to 'size_t' from 'int' may change the sign of the result [-Wsign-conversion]

为解决这个问题，我想将转换包装到一个函数中，该函数首先检查转换是否有效，然后进行强制转换.

To solve this, I would like to wrap the conversion in a function that first checks if the conversion is valid, then does the cast.

这是我到目前为止所拥有的:

This is what I have so far:

/* Convert int src to size_t dst. */
/* Assumes dst points to valid size_t address. */
int safe_size_t_from_int(size_t *dst, int src) {
    if(src < 0) return SAFE_ERROR_NEGATIVE;
    if(SIZE_MAX < INT_MAX) {
        if(src > (int)SIZE_MAX) return SAFE_ERROR_OVERFLOW;
    }
    *dst = (size_t)src;
    return SAFE_SUCCESS;
}

我错过了什么吗?是否已经存在具有安全转换的库?

Am I missing anything? Is there a library with safe conversions that already exists?

我能找到的最接近的东西是

The closest thing I can find is Microsoft Intsafe.h, but it appears to be for Win32 types only.

编辑已根据chux的评论进行了修改.

EDIT Modified as per chux' comment.

推荐答案

为避免在GCC中出现编译器警告，请将单个强制转换操作执行的操作限制为以下操作之一:

To avoid compiler warnings in GCC, limit the action performed by a single cast operation to one of the following:

1. 截断或扩展
2. 放弃有签名或无签名
3. 放弃常态或非常态

size_t始终是一个无符号类型，其大小足以容纳void指针.从铸造将int转换为size_t涉及两个强制转换操作:扩展，然后强制丢弃带符号的字符.

size_t is always an unsigned type large enough to hold a void pointer. Casting from int to size_t involves two cast operations: extend, then cast away signed-ness.

这里有两个函数在GCC 4.8.3上不产生编译器警告(带有'-Wall -Werror -Wextra').它们以内联方式(通过哨兵值)返回失败，而不是通过额外的返回参数返回.

Here's two functions that produce no compiler warnings (with '-Wall -Werror -Wextra') on GCC 4.8.3. They return failure inline (via sentinel values), rather than in an extra return parameter.

int size_t2int(size_t val) {
    return (val <= INT_MAX) ? (int)((ssize_t)val) : -1;
}

size_t int2size_t(int val) {
    return (val < 0) ? __SIZE_MAX__ : (size_t)((unsigned)val);
}

这篇关于如何安全地从int转换为size_t?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！