c - 如何在 C 中构造并返回字符串？

Question

这个问题已经有答案了:

Function returning address of local variable error in C (3 个回答)

已关闭 5 年前。

我正在尝试用 C 构造并返回一个字符串，但遇到了 function returns address of local variable [-Wreturn-local-addr]编译器警告。我得到了返回packet就像我想做的那样是行不通的，因为数据包是指向大小为 packet_size 的字符开头的指针，并且该内存地址在我的函数之外无效。我在 AVR 芯片上运行，不想使用 malloc 。我应该如何解决这个问题？

#include <stdio.h>
#include <string.h>
#include <stdint.h>

const char* construct_packet(const char* data);
void append(char* str, char c);

int main()
{
    const char* my_packet = construct_packet("QERT");
    printf("%s", my_packet);

    return 0;
}

const char* construct_packet(const char* data)
{
    const char training_chars[] = "___";
    const char start_char = '>';
    uint8_t checksum = 0;
    for(uint16_t i = 0; i < strlen(data); i++) {
        checksum += data[i];
    }
    const char checksum_char = checksum;

    uint8_t packet_size = strlen(training_chars) + strlen(data) + 2; // Plus 2 for start byte and checksum byte
    char packet[packet_size];

    strcat(packet, training_chars);
    append(packet, start_char);
    strcat(packet, data);
    append(packet, checksum_char);

    return packet;
}

void append(char* str, char c)
{
    str[strlen(str) + 1] = c;
}

Answer 1

如果您不想使用动态内存分配，也不想使用静态缓冲区，那么您可以尝试在堆栈上计算并提供内存缓冲区:

#include <stdio.h>
#include <string.h>
#include <stdint.h>

const char* construct_packet(const char* data, const char* training_chars, const char start_char, char* packet);
void append(char* str, char c);

int main()
{
    const char data[] = "QERT";
    const char training_chars[] = "___";
    const char start_char = '>';
    const uint8_t packet_size = strlen(training_chars) + strlen(data) + 2; // Plus 2 for start byte and checksum byte
    char packet[packet_size];

    const char* my_packet = construct_packet(data, training_chars, start_char, packet);
    printf("%s", my_packet);  // same as printf("%s", packet);

    return 0;
}

const char* construct_packet(const char* data, const char* training_chars, const char start_char, char* packet)
{
    uint8_t checksum = 0;
    for(uint16_t i = 0; i < strlen(data); i++) {
        checksum += data[i];
    }
    const char checksum_char = checksum;

    strcat(packet, training_chars);
    append(packet, start_char);
    strcat(packet, data);
    append(packet, checksum_char);

    return packet;
}

void append(char* str, char c)
{
    str[strlen(str) + 1] = c;
}