下面是一个例子：`

#include <stdio.h>
#include <string.h>
int main()
{
    char s1[] = "abcd", c;
    scanf("%c", c);
    char* pToC = strchr(s1, c);
    if (pToC)
    {
        if (*(pToC - 1) == a)
        {
            printf("%c", c);
        {
    }
return 0;
}

'在这种情况下，如果我输入“a”会发生什么？我的程序中也有类似的情况，我正在考虑会发生什么。在我的程序中，我必须检查strstr（）找到的单词前面是否有空格，但strstr（）的结果也可能指向字符串的第一个字符。
我期望它只在我输入“B”的时候才能工作。
编辑：由于注解有最大字符数限制，我将把确切的代码放在这里

#include <stdio.h>
#include <memory>

char* WordReplace(char* input, const char* word, const char* replacement)//EXERCISE 13
{
    if (input == 0 || *input == 0 || word == 0 || *word == 0 || replacement == 0 || *replacement == 0)
    {
        return 0;
    }
    int inputLength = strlen(input), wordLength = strlen(word), replacementLength = strlen(replacement);
    char* buffer = input;
    while (strstr(buffer, word))
    {
        char* firstChar = strstr(buffer, word), * nextChar = strstr(buffer, word) + wordLength;
        if ((firstChar == input && *nextChar == ' ') ||
            (firstChar == input && *nextChar == 0) ||
            (*(firstChar - 1) == ' ' && *nextChar == ' ') ||
            (*(firstChar - 1) == ' ' && *nextChar == 0))
        {
            buffer = strstr(buffer, word);
            char* output = (char*)malloc(sizeof(char) * (inputLength - wordLength + replacementLength + 1));
            memmove(output, input, sizeof(char) * (buffer - input));
            if (buffer != input)
            {
                output[buffer - input - 1] = ' ';
            }
            output[buffer - input] = 0;
            strcat(output, replacement);
            strcat(output, buffer + wordLength);
            return output;
        }
        buffer = strstr(buffer, word) + 1;
    }
    return 0;
}

int main()
{
    char thirteenInput[] = "My name is Karl", thirteenWord[] = "My", thirteenReplacement[] = "Your";//INPUT
    printf("WordReplace\n%s, %s, %s\n", thirteenInput, thirteenWord, thirteenReplacement);
    char* thirteenOutput = WordReplace(thirteenInput, thirteenWord, thirteenReplacement);
    if (thirteenOutput)
    {
        printf("%s\n\n", thirteenOutput);
        free(thirteenOutput);
    }
    else
    {
        printf("Word was not found / input error!\n\n");
    }
    return 0;
}