调用一个函数在c中的另一个函数调用中返回一个字符串

I am currently working on a program with the Dante *lyn II board from audinate. I am trying to use a void return function from the Dante API - foo() - that needs to have 3 various structs passed in as well as 2 strings. I have another function get_value_by_key() which returns the string value that I need. I initially tried calling on the program like so:

我目前正在与audinate的Dante *lyn II董事会合作开展一项计划。我试图使用Dante API中的void返回函数 - foo（） - 需要传入3个不同的结构以及2个字符串。我有另一个函数get_value_by_key（），它返回我需要的字符串值。我最初尝试这样调用该程序：

    foo(struct, struct, struct, get_value_by_key(key1), get_value_by_key(key2);

When I run it this way, the program twists the returned strings of get_value_by_key() and crashes the entire program. I have, however, found an alternative that works, but it is longer and I would like to not waste the extra processing power. The alternative is here:

当我以这种方式运行时，程序会扭曲返回的get_value_by_key（）字符串并使整个程序崩溃。但是，我发现了一种可行的替代方案，但它更长，我不想浪费额外的处理能力。替代方案是：

    char value1[15], value2[15];
    strcpy(value1, get_value_by_key(key1));
    strcpy(value2, get_value_by_key(key2));
    foo(struct, struct, struct, value1, value2);

I cant seem to decipher why the *lyn board shuts down with the first command, and not the second. Any help at all would be much appreciated. This is the code for get_value_key(). Pretty simple logic here:

我似乎无法破译为什么布鲁克林董事会用第一个命令关闭，而不是第二个命令。任何帮助都将非常感激。这是get_value_key（）的代码。这里很简单的逻辑：

    char * get_value_by_key(command_t command, char key[50]){
         int i;
         char value[50];
         for(i = 0; i < NUM_PARAMETERS; i++){
             if(strcmp(user_command.command_parameter[i].key, key) == 0){
                 strcpy(value, user_command.command_parameter[i].value);
             }
         }
         return value;
     }

2 个解决方案

#1

Your get_value_by_key function is broken -- it is returning a pointer to a local variable (value) which is destroyed when the function returns. So you get undefined behavior when you try to read the string -- it might still be there but might have been overwritten by something else.

你的get_value_by_key函数被破坏 - 它返回一个指向局部变量（值）的指针，该函数在函数返回时被销毁。因此，当您尝试读取字符串时，您会得到未定义的行为 - 它可能仍然存在，但可能已被其他内容覆盖。

#2

This looks like a mistake:

这看起来像是一个错误：

char * value1, value2; /* value1 is a char*, value2 is a char */
strcpy(value1, get_value_by_key(key1));
strcpy(value2, get_value_by_key(key2));

You are copying data into value1 and value2, but you have not allocated memory for the strings - just the pointer and the char. NOTE: only value1 is a char*, and value2 is a single char. If you want to declare both a char*, you need to write:

您正在将数据复制到value1和value2，但您没有为字符串分配内存 - 只是指针和char。注意：只有value1是char *，value2是单个char。如果你想声明两个char *，你需要写：

char *value1, *value2;

The code below should work without crashing (assuming get_value_by_key() returns a char*), but I don't know how you want to allocate the space. On the stack, the heap or in static RAM ?

下面的代码应该不会崩溃（假设get_value_by_key（）返回一个char *），但我不知道你想如何分配空间。在堆栈上，堆还是在静态RAM中？

char value1[128], value2[128];
strcpy(value1, get_value_by_key(key1));
strcpy(value2, get_value_by_key(key2));

EDIT: (edited after new info in the comments)

编辑:(在评论中的新信息后编辑）

Please post the code for get_value_by_key.

请发布get_value_by_key的代码。

I am betting it uses a static buffer to hold the string/char-array it returns a pointer to. That would mean the content gets destroyed after the second call and that could be a problem.

我打赌它使用一个静态缓冲区来保存字符串/ char-array，它返回一个指针。这意味着内容在第二次调用后被破坏，这可能是个问题。

EDIT2:

EDIT2：

If that is indeed the real source, then you are returning a pointer to something allocated on the stack - strictly verboten!!

如果那确实是真正的来源，那么你将返回一个指向堆栈上分配的东西的指针 - 严格的verboten !!

See returning a local variable from function in C

请参阅从C中的函数返回局部变量

#1

#2