如何将char数组转换为单个整数？ [英] how to cast an array of char into a single integer number?

问题描述

我正在尝试读取PNG文件的内容。

i'm trying to read contents of PNG file.

您可能知道，所有数据都以4字节的方式写入png文件，包括文本和数字。所以如果我们有编号35234它以这种方式保存：
[1000] [1001] [1010] [0010]。

As you may know, all data is written in a 4-byte manner in png files, both text and numbers. so if we have number 35234 it is save in this way: [1000][1001][1010][0010].

但有时数字更短，所以第一个字节是零，当我读取数组，并把它从char *到整数，我得到错误的数字。例如
有时数字被错误地解释为负数并且时间为零！

but sometimes numbers are shorter, so the first bytes are zero, and when I read the array and cast it from char* to integer I get wrong number. for example [0000] [0000] [0001] [1011] sometimes numbers are misinterpreted as negative numbers and simetimes as zero!

让我给你一个直观的例子：

let me give you an intuitive example:

char s_num[4] = {120, 80, 40, 1};

int  t_num = 0;

t_num = int(s_num);

我希望我能很好地解释我的问题！

I wish I could explain my problem well!

如何将这样的数组转换为单个整数值？

how can i cast such arrays into a single integer value?

ok ok确定，让我更改我的代码来解释它更好：

ok ok ok, let me change my code to explain it better:

char s_num[4] = {0, 0, 0, 13};
int  t_num;


t_num = *((int*) s_num);
cout << "t_num: " << t_num << endl;

这里我们得到13结果，
但是再次用这个新的解决方案的答案是错误的，你可以在你的电脑上测试！
我得到这个数字：218103808这是绝对错了！

here we have to get 13 as the result, ok? but again with this new solution the answer is wrong, you can test on your computers! i get this number:218103808 which is definitely wrong!

推荐答案

you cast（char *）to（int）。你应该做的是将指针转换为整数，例如这样：

you cast (char*) to (int). What you should do is cast to pointer to integer, ie something like this:

t_num = *((int*) s_num));

但你真的应该把你的代码提取到自己的函数中，并确保

But really you should extract your code into it's own function and make sure that

1. 字元序列正确


2. sizeof（int）== 4


3. 新C ++类型

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