Question

我正在使用带有CLR的Visual Studio 2010（公共语言运行时）。我想将unsigned char *从compress函数返回到main函数，但是unsigned char *和char *都给erro

“错误7错误C2440：'='：无法从'char *'转换为'unsigned char *'F：\ 4-2 \ Thesis \ PROJECT \ Database Compression Main \ Database Compression 2 \ db_comp_main.cpp 21”

unsigned char* compressor(char *data)
{
    unsigned char *compressed_string;
    //With some process I had compressed string of data variable as unsigned char* in variable compressed_string successfully and also printed here. Now want to return it from here.
    return compressed_string;
}
int main()
{ 
  unsigned char *main_data; 
  main_data=compressor("Muhammad Ashikuzzaman.Student from Khulna University Of Engineering And Technology from Bangladesh");// When I click the error from error list the cursor is put here beside str by visual studio.
  printf("%s",main_data);
}

需要从压缩器函数返回unsigned char *类型数据。请帮忙。

Answer 1

更改任何数据类型（函数参数*data或局部变量*main_data）以匹配类型。试试这个

unsigned char *main_data;

或者....

简单的类型转换可以使其正常工作：

unsigned char* compressor(char *data)
{
    unsigned char *compressed_string;
    compressed_string = (unsigned char*) data;
    return compressed_string;
}
int main()
{
  char *main_data;
  main_data=(char*) compressor("Muhammad Ashikuzzaman.Student from Khulna University Of Engineering And Technology from Bangladesh");
  printf("%s",main_data);
}

或......

（使用char*更改所有内容）

有三种字符类型:(普通）char，signed char和unsigned char。任何char通常是一个8位整数*（C语言中没有专用的“字符类型”）从这个意义上讲，signed和unsigned char具有有用的含义（通常等价到uint8_t和int8_t）。当用作文本意义上的字符时，请使用char（也称为普通字符）。这通常是signed char，但可以由编译器以任一方式实现。所以我认为在这里使用char*是安全的。

工作示例（将char *视为数据类型）：

char* compressor(char *data)
{
    char *compressed_string;
    compressed_string = "compressed";
    // compressed_string = data;
    return compressed_string;
}
int main()
{ 
  char *main_data; 
  main_data=compressor("Muhammad Ashikuzzaman.Student from Khulna University Of Engineering And Technology from Bangladesh");
  printf("%s",main_data);
}

另外，为简单起见，您可以使用指针指向

void compressor(char **data) {
    *data = "compressed"; // assuming the compressed data will be smaller in length of main data, so buffer overflow won't occur  
}

int main() {
    char *main_data = "Muhammad Ashikuzzaman.Student from Khulna University Of Engineering And Technology from Bangladesh";
    compressor(&main_data);
    printf("%s", main_data);
    return 0;
}

修改

当你问一个通过引用传递的替代方法时，除了通过引用传递之外没有办法将数组作为函数参数传递。因为当您编写void func(char str[])时，您可能会认为您正在执行按值传递。但是g ++编译器会将语句优化为void func(char &str[0])，以避免将整个数组作为函数参数进行处理。因此，在所有情况下，您实际上是通过引用传递的。

Answer 2

这里你必须为字符串分配内存存储空间。指针只指向一个字节而不是像array一样的字节序列。你必须使用calloc或malloc作为C和new来为C ++分配所需的内存地址。使用类型转换将char *转换为unsigned char *。

#include <bits\stdc++.h>
unsigned char* compressor(unsigned char *data)
{
    unsigned char *compressed_string = new unsigned char[100];
    //With some process I had compressed string of data variable as unsigned unsigned char** in variable compressed_string successfully and also printed here. Now want to return it from here.
    compressed_string = (unsigned char*)"working";
    return compressed_string;
}
int main()
{
  unsigned char *main_data = new unsigned char[1000];
  main_data=compressor((unsigned char*)"Muhammad Ashikuzzaman.Student from Khulna University Of Engineering And Technology from Bangladesh");// When I click the error from error list the cursor is put here beside str by visual studio.
  printf("%s",main_data);
}

您可以根据需要使用不同的输入变量来使用内存，以避免不必要的动态分配。

#include <bits\stdc++.h>
unsigned char* compressor(unsigned char *data) {
    unsigned char *compressed_string = new unsigned char[strlen((char*)data)+1];
    //With some process I had compressed string of data variable as unsigned char* in variable compressed_string successfully and also printed here. Now want to return it from here.
    compressed_string = (unsigned char*)"working";
    return compressed_string;
}
int main() {
    unsigned char *inp = new unsigned char[1000];
    inp = (unsigned char*)"Muhammad Ashikuzzaman.Student from Khulna University Of Engineering And Technology from Bangladesh";
    unsigned char *main_data = new unsigned char[strlen((char*)inp)+1];
    main_data = compressor(inp);
    printf("%s",main_data);
}

unsigned char * data作为c ++或c中函数的返回类型

2 个答案: