c - 为什么 fprintf 会打印额外的值

Question

为了 Protocol Buffer 的目的，我想对包含字段编号和线路类型的标签进行编码。我现在遇到的问题是，每当我的“标签”值低于“8”时，fprintf 都会在正确的值旁边写入其他值。即它打印 38c0 3 而不是 38。如果 tag 的值为 8 或更高，脚本工作正常。下面是省略了无关行的代码。

int uint32_pack (uint8_t *fieldnumber, uint32_t value, uint8_t *out);

int main(){

uint32_t initvalue = 2;
int return_rv;
uint8_t *tag = (uint8_t *) malloc(sizeof(uint8_t));    
uint8_t *tempout= (uint8_t *) malloc(sizeof(uint32_t));
*tag = 7; //value to be encoded (won't work for values less than 8)

return_rv = uint32_pack (tag, initvalue, tempout);

free(tempout);

    }

/* === pack() === */
/* Pack an unsigned 32-bit integer in base-128 encoding, and return the number
 of bytes needed: this will be 5 or less. */

int uint32_pack (uint8_t *fieldnumber, uint32_t value, uint8_t *out)
{
  unsigned rv = 0;
  FILE *wiretypetag;
  int secondaryvalue;

  wiretypetag = fopen("wiretype.txt","w");


    //encodes wire type and the field number
    if (*fieldnumber <16){
       *fieldnumber <<= 3;
       fprintf(wiretypetag,"%x",fieldnumber[0]);
       }
    if (*fieldnumber < 32 && *fieldnumber > 15){
       *fieldnumber <<= 3;
       secondaryvalue = 0x01;
       fprintf(wiretypetag,"%x %x",fieldnumber[0],secondaryvalue);
           }
    if (*fieldnumber < 48 && *fieldnumber > 31){
        *fieldnumber += 0x10;
        *fieldnumber &= 0x1F;
        *fieldnumber <<= 3;
        secondaryvalue = 0x02;
        fprintf(wiretypetag,"%x %x",fieldnumber[0], secondaryvalue);
        }       
    if (*fieldnumber < 64 && *fieldnumber > 47){
        *fieldnumber &= 0x1F;
        *fieldnumber <<= 3;
        secondaryvalue = 0x03;
        fprintf(wiretypetag,"%x %x",fieldnumber[0], secondaryvalue);
        }       

  /* assert: value<128 */   
    out[rv++] = value;


    if (rv == 1){         
           fprintf(outfile,"%x",out[0]);
           }
    if (rv == 2){
           fprintf(outfile,"%x %x",out[0], out[1]);
           }    
    if (rv == 3){
           fprintf(outfile,"%x %x %x",out[0],out[1],out[2]);
           }
    if (rv == 4){
           fprintf(outfile,"%x %x %x %x",out[0],out[1],out[2],out[3]);
           }
    if (rv == 5){
           fprintf(outfile,"%x %x %x %x %x",out[0],out[1],out[2],out[3],out[4]);
           }

    fclose(wiretypetag);

    return rv;
}

Answer 1

 if (fieldnumber <16){

应该是

if (*fieldnumber <16){