在 C 中构造字符串

Question

这是我用来从char数组构造字符串的演示代码，有没有更好的方法来构造字符串*RV200#*FV200#？？

int main()
{    
char String4H1[10] = "*FV";
char String4H3[10] = "*RV";
char String4H2[10] = "#";

char data1[10];
char data2[10];

snprintf(data1,4, "%03d", 200); //Convert integer to string function
snprintf(data2,4, "%03d", 200); //Convert integer to string function

ConvertToString(String4H1,data1, 3);     //*FV200
ConvertToString(String4H3,data2, 3);     //*RV200

ConvertToString(String4H1,String4H2,6);   //*FV200#
ConvertToString(String4H3,String4H2,6);   //*RV200#

//Display String4H1 And String 4H3 

}


void ConvertToString(char subject[], const char insert[], int pos) 
{
char buf[100] = {};  
strncpy(buf, subject, pos);               // copy at most first pos characters
int len = strlen(buf);
strcpy(buf+len, insert);                 // copy all of insert[] at the end
len += strlen(insert);                  // increase the length by length of insert[]
strcpy(buf+len, subject+pos);          // copy the rest

strcpy(subject, buf);                 // copy it back to subject
                                 // deallocate buf[] here, if used malloc()
}

数字200在程序开始时是未知的，它是使用IDE函数从内存中获取的，以从特定的内存地址获取值。 像这样：-

unsigned short BUF = GetWord(@FrontVIB@,0);    
unsigned short BUF1 = GetWord(@RearVIB@,0);

//BUF and BUF1 stores the value of address @FrontVIB@ and @RearVIB@ respectively

**structure** :-
unsigned short GetWord( @Address Alias@, Address Offset );

Answer 1

这是一个简单的例子。可能我会被否决:)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

bool concatenateString(char **dest, size_t *size, char *stringToAdd)
{
    bool retVal = true;
    char *dest_old = *dest;

    *size += strlen(stringToAdd);

    if (*dest == NULL)
    {
        *size += 1; // to add null terminator of string
        *dest = calloc(1, size);
    }
    else
    {
        *dest = realloc(*dest, size);
    }

    if (dest == NULL)
    {
        free(dest_old);
        retVal = false;
    }
    else
    {
        strcat(*dest, stringToAdd);
    }

    return retVal;
}

int main()
{
    char newString[32] = {0};
    int number;
    size_t size = 0;

    char *data1 = NULL;

    printf("Insert a string:");
    scanf(" %s", newString);
    if (concatenateString(&data1, &size, newString))
    {
        printf("Insert a number:");
        scanf(" %d", &number);
        sprintf(newString, "%03d", number);
        if (concatenateString(&data1, &size, newString) )
        {
            printf("Insert a string:");
            scanf(" %s", newString);
            if (concatenateString(&data1, &size, newString))
               printf("%s\n", data1);
        }
    }

    free(data1);
}

不使用动态分配

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

bool concatenateString(char *dest, size_t size_of_dest, char *stringToAdd)
{
    bool retVal = true;

    size_t new_size = strlen(dest) + strlen(stringToAdd);

    if (new_size < size_of_dest)    
    {
        strcat(dest, stringToAdd);
    } 
    else
    {
        retVal = false;
    }
    return retVal;
}

int main()
{
    char result[128] = {0};
    char newString[32] = {0};
    int number;

    printf("Insert a string:");
    scanf(" %s", newString);
    printf("%s\n", newString);
    if (concatenateString(result, sizeof(result), newString))
    {
        printf("Insert a number:");
        scanf(" %d", &number);
        sprintf(newString, "%03d", number);
        if (concatenateString(result, sizeof(result), newString) )
        {
            printf("Insert a string:");
            scanf(" %s", newString);
            if (concatenateString(result, sizeof(result), newString))
               printf("%s\n", result);
        }
    }
}

输入

Insert a string: *RV
Insert a number: 200
Insert a string: #

输出

*RV200#

Answer 2

一些问题，我只处理ConvertToString()

---

尽管在处理字符串缓冲区问题方面进行了一些尝试，但 OP 的代码中存在太多漏洞。请考虑以下内容。

void ConvertToString(char subject[], const char insert[], int pos) {
  char buf[100] = {};  
  strncpy(buf, subject, pos);               // copy at most first pos characters
  int len = strlen(buf);
  ...

pos == 100 有什么影响？
strlen(buf) 可能会尝试查找不包含空字符的字符数组的长度 --> UB。

pos > 100 的影响是什么？
strncpy() 尝试在buf 的绑定之外写入数据。

Pedantic：pos < 0 的影响是什么？
strncpy() 尝试在buf 的绑定之外写入数据，因为pos 被转换为一个过大的无符号数。

---

关于strcpy(buf+len, subject+pos);

如果pos超过strlen(subject)会有什么影响
UB 作为代码尝试在 subject 之外读取。

---

重写尝试。关键元素：包括可用于扩展的subject 的大小并确定字符串长度。然后测试可接受性。毕竟，移动subject 的结尾，为insert 腾出空间。

void ConvertToString(char subject[], size_t subject_size, const char *insert,
    size_t pos) {

  size_t insert_length = strlen(insert);
  size_t subject_length = strlen(subject);
  // Insure pos does not exceed subject_length, 
  // this critical part missing in OP code 
  if (pos > subject_length) {
    pos = subject_length;
  }

  // Insure we have enough space
  size_t buf_size = subject_length + insert_length + 1;
  if (buf_size > subject_size) {
    Handle_Insufficent_subject_size();
    return;
  }
  // Move end portion of `subject` over to the right `insert_length` places.
  memmove(subject + pos + insert_length, subject + pos, subject_length - pos + 1);
  memcpy(subject + pos, insert, insert_length); // copy insert
}