sprintf()疯了

Question

我需要一些帮助,因为它让我的C程序感到困惑

我有2个字符串(基数和路径)

BASE: /home/steve/cps730
PATH: /page2.html

这就是printf在我调用sprintf将它们的内容连接在一起之前读取的方式.这是代码块

        int memory_alloc = strlen(filepath)+1;
        memory_alloc += strlen(BASE_DIR)+1;
        printf("\n\nAlloc: %d",memory_alloc);
        char *input = (char*)malloc(memory_alloc+9000);
        printf("\n\nBASE: %s\nPATH: %s\n\n",BASE_DIR,filepath);
        sprintf(input, "%s%s",BASE_DIR,filepath); //   :(

        printf("\n\nPATH: %s\n\n",input);

现在,您能解释一下最终的printf语句是如何返回的

PATH: e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/stev

因为它根本不理解它.

**我在malloc语句中添加了9000以防止程序崩溃(因为字符串的大小明显大于31个字节.

全输出

Alloc: 31

BASE: /home/steve/cps730
PATH: /page2.html



PATH: /home/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/steve/cps730e/stev

Sending: 
HTTP/1.0 404 Not Found
Date: Sat, 12 Sep 2009 19:01:53 GMT
Connection: close

编辑...................使用这些变量的所有代码

const char *BASE_DIR = "/home/steve/cps730";
 char* handleHeader(char *header){
    //Method given by browser (will only take GET, POST, and HEAD)
    char *method;
    method = (char*)malloc(strlen(header)+1);
    strcpy(method,header);
    method = strtok(method," ");

    if(!strcmp(method,"GET")){
        char *path = strtok(NULL," ");
        if(!strcmp(path,"/")){
            path = (char*)malloc(strlen(BASE_DIR)+1+12);
            strcpy(path,"/index.html");
        }
        free(method);
        return readPage(path);
    }
    else if(!strcmp(method,"POST")){

    }
    else if(!strcmp(method,"HEAD")){

    }
    else{
        strcat(contents,"HTTP/1.1 501 Not Implemented\n");
                strcat(contents, "Date: Sat, 12 Sep 2009 19:01:53 GMT\n");
                strcat(contents, "Connection: close\n\n");
    }
    free(method);

}

//Return the contents of an HTML file
char* readPage(char* filepath){
    int memory_alloc = strlen(filepath)+1;
    memory_alloc += strlen(BASE_DIR)+1;
    printf("\n\nAlloc: %d",memory_alloc);
    char *input = (char*)malloc(memory_alloc+9000); 
    printf("\n\nBASE: %s\nPATH: %s\n\n",BASE_DIR,filepath);
    sprintf(input, "%s%s\0",BASE_DIR,filepath);

    printf("\n\nPATH: %s\n\n",input);

    FILE *file;
    file = fopen(input, "r");
    char temp[255];
    strcat(contents,"");

    if(file){
        strcat(contents, "HTTP/1.1 200 OK\n");
                strcat(contents, "Date: Sat, 12 Sep 2009 19:01:53 GMT\n");
                strcat(contents, "Content-Type: text/html; charset=utf-8\n");
                strcat(contents, "Connection: close\n\n");

        //Read the requested file line by line
        while(fgets(temp, 255, file)!=NULL) { 
            strcat(contents, temp);         
        }
    }
    else{
        strcat(contents, "HTTP/1.0 404 Not Found\n");
                strcat(contents, "Date: Sat, 12 Sep 2009 19:01:53 GMT\n");
                strcat(contents, "Connection: close\n\n");
    }

    return contents;
}

Answer 1

readPage使用无效指针调用path- 它指向先前使用method指针分配的内存,该指针在调用之前被释放readPage.接下来malloc可以重用这个内存然后发生任何事情...