使用 strncat 进行字符串连接会导致符号错误
更新：关于 char、signed char 还是 unsigned 的问题最终没有意义。在这种情况下使用 memcpy 更合适，因为它在字节上不加区别地工作。
不可能是一个更简单的操作，但我似乎错过了一个关键步骤。在下面的代码中，我尝试用 buffer 填充 bufferdata，编译器会警告我符号性存在差异。
unsigned char buffer[4096] = {0};
char *bufferdata;
bufferdata = (char*)malloc(4096 * sizeof(bufferdata));
if (! bufferdata)
return false;
while( ... )
{
// nextBlock( voidp _buffer, unsigned _length );
read=nextBlock( buffer, 4096);
if( read > 0 )
{
bufferdata = strncat(bufferdata, buffer, read); // (help)
// leads to: pointer targets in passing argument 2 of strncat differ in signedness.
if(read == 4096) {
// let's go for another chunk
bufferdata = (char*)realloc(bufferdata, ( strlen(bufferdata) + (4096 * sizeof(bufferdata)) ) );
if (! bufferdata) {
printf("failed to realloc\n");
return false;
}
}
}
else if( read<0 )
{
printf("error.\n");
break;
}
else {
printf("done.\n");
break;
}
}
update: the point of whether char, signed char, or unsigned was ultimately moot here. it was more appropriate to use memcpy in this situation, since it works indiscriminately on bytes.
Couldn't be a simpler operation, but I seem to be missing a critical step. In the following code, I am attempting to fill bufferdata with buffer for which the compiler warns me of a difference in signedness.
unsigned char buffer[4096] = {0};
char *bufferdata;
bufferdata = (char*)malloc(4096 * sizeof(bufferdata));
if (! bufferdata)
return false;
while( ... )
{
// nextBlock( voidp _buffer, unsigned _length );
read=nextBlock( buffer, 4096);
if( read > 0 )
{
bufferdata = strncat(bufferdata, buffer, read); // (help)
// leads to: pointer targets in passing argument 2 of strncat differ in signedness.
if(read == 4096) {
// let's go for another chunk
bufferdata = (char*)realloc(bufferdata, ( strlen(bufferdata) + (4096 * sizeof(bufferdata)) ) );
if (! bufferdata) {
printf("failed to realloc\n");
return false;
}
}
}
else if( read<0 )
{
printf("error.\n");
break;
}
else {
printf("done.\n");
break;
}
}
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显然，在您的编译器中，
char是signed char，因此出现警告消息。Obviously in your compiler
charissigned char, thus the warning message.因此，由于您的目标缓冲区是无符号字符，因此会出现符号警告。如果不需要签名，您可以将缓冲区更改为 char 数组，否则您可以在编译器中使用 -w 选项忽略警告。
so as your destination buffer is unsigned char so there will be a warning of sign. You can either change your buffer to char array if signed is not necessary else you can ignore warnings using -w option in compiler.