c - malloc 问题导致变量被覆盖

Question

我的程序中有 3 个全局变量。出于某种原因，当我在 pad 上运行 string2bin 时，binaryMessage 的内容被覆盖了，我不知道为什么。我增加了我的 malloc 的大小，但这没有帮助。我做错了什么？

请注意，randomPad() 创建一串随机“十六进制”值，应将其转换为表示十六进制字符串的二进制字符串。

char * temp;
char * binaryMessage;
char * pad;

void process_message(char *s)

int main (int argc, const char * argv[]) {

        temp = (char *)malloc(sizeof(char *) *2048);

        binaryMessage = (char *)malloc(sizeof(char *) *2048);

        pad = (char *)malloc(sizeof(char *) * 2048);

        process_message("test");

}


char * char2bin ( unsigned char c ){
      static char bin[CHAR_BIT + 1] = {0};
      int i;

       for ( i = CHAR_BIT - 1; i >= 0; i-- ) {
            bin[i] = (c % 2) + '0';
            c /= 2;
       }

       return bin;
}

char* string2bin(char* str){
       int i;
       int len = strlen(str);

       sprintf(temp,"");
       for(i=0; i< len;i++){
             sprintf(temp, "%s%s",temp,char2bin(str[i]));
       }
       return temp;
 }

 char* randomPad(){
       int i;
       const char *hex_digits = "0123456789ABCDEF";
       char * p = (char*)malloc(sizeof(char*)*242);

       // clear old pad data
       //sprintf(pad,"");

       // create random string of 242 hex chars to use as pad
       for(i = 0; i< 242; i++){
             sprintf(p,"%s%c",p,hex_digits[ ( rand() % 16 ) ]);
       }
       return p;
 }
 void process_message(char *s){
       binaryMessage = string2bin(s);
       printf("m %s\nbm %s\n",s, binaryMessage);

       //get random one time pad
       pad = string2bin(randomPad());

       printf("m %s\nbm %s\n",s, binaryMessage);
 }

我的预期输出是:

m test
bm 01110100011001010111001101110100
m test
bm 01110100011001010111001101110100

我的实际输出是:

m test
bm 01110100011001010111001101110100
m test
bm 0011011100110001001110010100000100110010001110000011100001000101001100110100010000111000001101010100001100110010001100110011011100110111001100010011100000110100010001100011000101000100001101010011100000110101010000100011011000111000001101110011100100110010001110000011001100110010001100010011001101000100001100110011010101000110001100000011000100111000010001000011000101000011010000100011001000110101001110010011000100110100001110000011010000110010010000110011010001000001001101110100000101000001001101010011100000111001001101010011000100110000001101000011010101000001001101010100001001000100001110010011011000110111001110000011000100110101001100110100010101000100001101010011010100110011001110010011010001000010010000010100001100110011001100010011001000110000010001010100001100110001001101100011100001000100001100010100011000110100001100010100010100111001010001000011011000110000001110010011011100110001010001100011001101000001010001010100011000110000010000110011010000110101010000010011100001000010001100000011100100110010010001010011001000110110001101010011001001000011010001100100010001000110001110000011011101000100010001010100011000110010001100010011000001000101001110000011011100110111010001010011010000110010001101110011011101000101001101110011000100111000001110010100010101000010001100100011010100110010001101100011011001000011001101000100010100110110010000010011001000110011001100100011010000110110001101100011011101000110001100110011100100110001001110000011001101000110001100010011100000110101010001100011010000110000001100000011011101000010001110010100010101000001010000100011011100111000010000110100011000110010010000110100001100110111010001100011000101000100001101010011000100110011001100010100000101000101001100110011000000110001001110010011000100110111010000110100001000111000010001100100011000110010001100110100001101000100001110000011000001000101001110000100001001000100010001100100011000110001001100010011000001000110

Answer 1

这些行很关键:

sprintf(temp, "%s%s", temp, char2bin(str[i]));

...

sprintf(p, "%s%c", p, hex_digits[ ( rand() % 16 ) ]);

来自 sprintf()'s man page :

Some programs imprudently rely on code such as the following

       sprintf(buf, "%s some further text", buf);

to append text to buf. However, the standards explicitly note that the results are undefined if source and destination buffers overlap when calling sprintf(), snprintf(), vsprintf(), and vsnprintf(). Depending on the version of gcc(1) used, and the compiler options employed, calls such as the above will not produce the expected results.