动态分配的C样式字符串具有比给定长度更多的字符？

Question

I'm using a dynamic C-style string to read in data from a file, but for some reason when I dynamically allocate the C-style string using the given length, it comes out with four extra characters that can be seen using strlen() . The junk in these empty spaces is added on to the end of the read-in string and is displayed on cout . What on earth could be causing this, and how can I fix it?

The C-style string is declared in the beginning of the code, and is used one time before this. The time it is used before this it is also too large, but in that case it does not add extra information to the end. After use, it is deleted and not used again until this point. I'm pretty confused as I have not had this happen or had a problem with it before.

// Length read as 14, which is correct
iFile.read(reinterpret_cast<char *>(&length), sizeof(int)); 

tempCstring = new char[length]; // Length still 14
cout << strlen(tempCstring); // Console output: 18

// In tempCstring: Powerful Blockýýýý
iFile.read(reinterpret_cast<char *>(tempCstring), length);

// Custom String class takes in value Powerful Blockýýýý and is 
// initialized to that
tempString = String(tempCstring);

// Temp character value takes in messed up string
temp.setSpecial(tempString); 
delete[] tempCstring; // Temp cString is deleted for next use

When written to file:

// Length set to the length of the cString, m_special
length = strlen(chars[i].getSpecial().getStr());

// Length written to file. (Should I add 1 for null terminator?)
cFile.write(reinterpret_cast<char *>(&length), sizeof(int));

// String written to file
cFile.write(reinterpret_cast<char *>(chars[i].getSpecial().getStr()), length);

Answer 1

Whenever you see junk at the end of a string, the problem is almost always the lack of a terminator. Every C-style string ends in a byte whose value is zero, spelled '\\0' . If you did not place one yourself, the standard library keeps reading bytes in memory until it sees a random '\\0' that it sees in memory. In other words, the array is read beyond its bounds.

Use memset(tempCString,0,length) in order to zero out the memory following your allocation. However, this is not the soundest solution, as it is covering the real problem under the rug. Show us the context in which this code is used. Then I will be able to say where in your algorithm you will need to insert the null terminator: tempCString[i] = 0 , or something like that. Nonetheless, from what you have posted, I can tell that you need to allocate one more character to make room for the terminator.

Also, since you are using C++, why not use std::string ? It avoids these kinds of problems.