sscanf() skipping delimiter & width
I am writing an assembler for 6502 and trying to read the instructions and opcode data from a file I prepared. Using sscanf to store data and it only worked partially...
File:
ADC,Im,69,2
ADC,ZP,65,2
ADC,ZPx,75,2
ADC,Ab,6D,3
ADC,Abx,7D,3
ADC,Aby,79,3
...
Here is only part of the code related to the problem. fgets works fine. Problem line commented below. Will upload more if needed.
Code:
FILE *fp = ...
char bf[15];
char name[3];
char mode[3];
char op[2];
int bytes;
while (fgets(bf,15,fp)) {
//below is the problem line
sscanf(bf, "%3[^,],%3[^,],%2[^,],%d", name, mode, op, &bytes);
}
printf("%s,%s,%s,%d\n", name, mode, op, bytes);
Output:
ADCIm,Im,69,2
ADCZP,ZP,65,2
ADCZPx75,ZPx75,75,2
ADCAb,Ab,6D,3
ADCAbx7D,Abx7D,7D,3
...
Expected to be (just like the file format):
ADC,Im,69,2
ADC,ZP,65,2
ADC,ZPx75,75,2
ADC,Ab,6D,3
ADC,Abx7D,7D,3
...
It seems that op and bytes all work alright, but there are something wrong with the name and mode variables, even though I contained the width and delimiter in the argument.
转载于:https://stackoverflow.com/questions/53147902/sscanf-skipping-delimiter-width
Actually, it's not sscanf that is at fault. You have undefined behavior due to buffer overruns -- printf knows nothing about the fact that your strings are not null-terminated, and it will continue printing characters until it finds a '\0'.
To stop it from doing that, you can supply a maximum field width in the format specifier:
printf("%.3s,%.3s,%.2s,%d\n", name, mode, op, bytes);